diff --git a/internal/service/file.go b/internal/service/file.go
new file mode 100644
index 0000000..826eb4b
--- /dev/null
+++ b/internal/service/file.go
@@ -0,0 +1,439 @@
+package service
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"time"
+
+	pb "rag/file-system/api/file/v1"
+	"rag/file-system/internal/biz"
+	"rag/file-system/internal/data"
+
+	"github.com/go-kratos/kratos/v2/log"
+	"google.golang.org/protobuf/types/known/emptypb"
+)
+
+// FileService implements the proto-generated FileServiceServer interface.
+type FileService struct {
+	pb.UnimplementedFileServiceServer
+
+	fileUC   *biz.FileUsecase
+	bucketUC *biz.BucketUsecase
+	folderUC *biz.FolderUsecase
+	shareUC  *biz.ShareUsecase
+	log      *log.Helper
+}
+
+// NewFileService creates a new FileService instance.
+func NewFileService(fileUC *biz.FileUsecase, bucketUC *biz.BucketUsecase, folderUC *biz.FolderUsecase, shareUC *biz.ShareUsecase, logger log.Logger) *FileService {
+	return &FileService{
+		fileUC:   fileUC,
+		bucketUC: bucketUC,
+		folderUC: folderUC,
+		shareUC:  shareUC,
+		log:      log.NewHelper(logger),
+	}
+}
+
+// --- File operations ---
+
+// UploadFile uploads file data to the specified bucket and key.
+func (s *FileService) UploadFile(ctx context.Context, req *pb.UploadFileRequest) (*pb.UploadFileResponse, error) {
+	err := s.fileUC.UploadFile(ctx, req.BucketName, req.ObjectKey, bytes.NewReader(req.Data))
+	if err != nil {
+		return nil, err
+	}
+	return &pb.UploadFileResponse{
+		Message:   "uploaded",
+		ObjectKey: req.ObjectKey,
+	}, nil
+}
+
+// DownloadFile downloads file data from the specified bucket and key.
+func (s *FileService) DownloadFile(ctx context.Context, req *pb.DownloadFileRequest) (*pb.DownloadFileResponse, error) {
+	body, err := s.fileUC.DownloadFile(ctx, req.BucketName, req.ObjectKey)
+	if err != nil {
+		return nil, err
+	}
+	defer body.Close()
+
+	fileData, err := io.ReadAll(body)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.DownloadFileResponse{
+		Data:        fileData,
+		ContentType: "application/octet-stream",
+		FileName:    req.ObjectKey,
+	}, nil
+}
+
+// ListFiles lists objects in a bucket with pagination.
+func (s *FileService) ListFiles(ctx context.Context, req *pb.ListFilesRequest) (*pb.ListFilesResponse, error) {
+	var token *string
+	if req.ContinuationToken != "" {
+		token = &req.ContinuationToken
+	}
+	result, err := s.fileUC.ListObjectsV2(ctx, req.BucketName, req.Prefix, req.MaxKeys, token)
+	if err != nil {
+		return nil, err
+	}
+
+	files := make([]*pb.FileInfo, 0, len(result.Files))
+	for _, f := range result.Files {
+		files = append(files, &pb.FileInfo{
+			Key:          f.Key,
+			Size:         f.Size,
+			LastModified: f.LastModified.Format(time.RFC3339),
+			Etag:         f.ETag,
+		})
+	}
+
+	resp := &pb.ListFilesResponse{Files: files}
+	if result.NextContinuationToken != nil {
+		resp.NextContinuationToken = *result.NextContinuationToken
+	}
+	return resp, nil
+}
+
+// GetFilePreview returns a presigned URL for file preview.
+func (s *FileService) GetFilePreview(ctx context.Context, req *pb.GetFilePreviewRequest) (*pb.GetFilePreviewResponse, error) {
+	url, err := s.fileUC.GetPreviewURL(ctx, req.BucketName, req.ObjectKey)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.GetFilePreviewResponse{PresignedUrl: url}, nil
+}
+
+// GetFileContent retrieves text content of a file for display.
+func (s *FileService) GetFileContent(ctx context.Context, req *pb.GetFileContentRequest) (*pb.GetFileContentResponse, error) {
+	content, err := s.fileUC.GetFileContent(ctx, req.BucketName, req.ObjectKey)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.GetFileContentResponse{Content: content}, nil
+}
+
+// DeleteFile removes a file from the specified bucket.
+func (s *FileService) DeleteFile(ctx context.Context, req *pb.DeleteFileRequest) (*emptypb.Empty, error) {
+	err := s.fileUC.DeleteFile(ctx, req.BucketName, req.ObjectKey)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// --- Multipart upload ---
+
+// InitMultipartUpload starts a multipart upload session.
+func (s *FileService) InitMultipartUpload(ctx context.Context, req *pb.InitMultipartRequest) (*pb.InitMultipartResponse, error) {
+	uploadID, err := s.fileUC.CreateMultipartUpload(ctx, req.BucketName, req.ObjectKey)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.InitMultipartResponse{UploadId: uploadID}, nil
+}
+
+// UploadPart uploads a single part in a multipart upload.
+func (s *FileService) UploadPart(ctx context.Context, req *pb.UploadPartRequest) (*pb.UploadPartResponse, error) {
+	etag, err := s.fileUC.UploadPart(ctx, req.BucketName, req.ObjectKey, req.UploadId, req.PartNumber, bytes.NewReader(req.Data))
+	if err != nil {
+		return nil, err
+	}
+	return &pb.UploadPartResponse{Etag: etag}, nil
+}
+
+// CompleteMultipartUpload assembles all uploaded parts.
+func (s *FileService) CompleteMultipartUpload(ctx context.Context, req *pb.CompleteMultipartRequest) (*pb.CompleteMultipartResponse, error) {
+	parts := make([]data.Part, 0, len(req.Parts))
+	for _, p := range req.Parts {
+		parts = append(parts, data.Part{
+			PartNumber: p.PartNumber,
+			ETag:       p.Etag,
+		})
+	}
+	location, err := s.fileUC.CompleteMultipartUpload(ctx, req.BucketName, req.ObjectKey, req.UploadId, parts)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.CompleteMultipartResponse{Location: location}, nil
+}
+
+// AbortMultipartUpload cancels a multipart upload session.
+func (s *FileService) AbortMultipartUpload(ctx context.Context, req *pb.AbortMultipartRequest) (*emptypb.Empty, error) {
+	err := s.fileUC.AbortMultipartUpload(ctx, req.BucketName, req.ObjectKey, req.UploadId)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// --- Bucket operations ---
+
+// CreateBucket creates a new S3 bucket.
+func (s *FileService) CreateBucket(ctx context.Context, req *pb.CreateBucketRequest) (*emptypb.Empty, error) {
+	err := s.bucketUC.CreateBucket(ctx, req.Name)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// ListBuckets returns all bucket names.
+func (s *FileService) ListBuckets(ctx context.Context, _ *emptypb.Empty) (*pb.ListBucketsResponse, error) {
+	buckets, err := s.bucketUC.ListBuckets(ctx)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.ListBucketsResponse{Buckets: buckets}, nil
+}
+
+// DeleteBucket removes an S3 bucket.
+func (s *FileService) DeleteBucket(ctx context.Context, req *pb.DeleteBucketRequest) (*emptypb.Empty, error) {
+	err := s.bucketUC.DeleteBucket(ctx, req.Name)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// --- Folder operations ---
+
+// CreateFolder creates a new folder under the given parent.
+func (s *FileService) CreateFolder(ctx context.Context, req *pb.CreateFolderRequest) (*pb.Folder, error) {
+	var parentID *string
+	if req.ParentId != "" {
+		parentID = &req.ParentId
+	}
+	folder, err := s.folderUC.CreateFolder(ctx, parentID, req.Name, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	return folderPOToProto(folder), nil
+}
+
+// GetFolderTree returns all folders owned by a user.
+func (s *FileService) GetFolderTree(ctx context.Context, req *pb.GetFolderTreeRequest) (*pb.GetFolderTreeResponse, error) {
+	folders, err := s.folderUC.GetFolderTree(ctx, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	pbFolders := make([]*pb.Folder, 0, len(folders))
+	for i := range folders {
+		pbFolders = append(pbFolders, folderPOToProto(&folders[i]))
+	}
+	return &pb.GetFolderTreeResponse{Folders: pbFolders}, nil
+}
+
+// GetFolder returns a folder with its children (sub-folders and files).
+func (s *FileService) GetFolder(ctx context.Context, req *pb.GetFolderRequest) (*pb.FolderWithChildren, error) {
+	folder, subFolders, files, err := s.folderUC.GetFolder(ctx, req.Id, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	if folder == nil {
+		return nil, nil
+	}
+
+	pbSubFolders := make([]*pb.Folder, 0, len(subFolders))
+	for i := range subFolders {
+		pbSubFolders = append(pbSubFolders, folderPOToProto(&subFolders[i]))
+	}
+	pbFiles := make([]*pb.FileMeta, 0, len(files))
+	for i := range files {
+		pbFiles = append(pbFiles, fileMetaPOToProto(&files[i]))
+	}
+
+	return &pb.FolderWithChildren{
+		Folder:     folderPOToProto(folder),
+		SubFolders: pbSubFolders,
+		Files:      pbFiles,
+	}, nil
+}
+
+// RenameFolder updates a folder's name.
+func (s *FileService) RenameFolder(ctx context.Context, req *pb.RenameFolderRequest) (*pb.Folder, error) {
+	folder, err := s.folderUC.RenameFolder(ctx, req.Id, req.Name, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	return folderPOToProto(folder), nil
+}
+
+// DeleteFolder removes a folder and all its descendant files.
+func (s *FileService) DeleteFolder(ctx context.Context, req *pb.DeleteFolderRequest) (*emptypb.Empty, error) {
+	err := s.folderUC.DeleteFolder(ctx, req.Id, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// UploadToFolder uploads a file into a folder with metadata tracking.
+func (s *FileService) UploadToFolder(ctx context.Context, req *pb.UploadToFolderRequest) (*pb.FileMeta, error) {
+	meta, err := s.folderUC.UploadToFolder(ctx, req.FolderId, req.FileName, req.Data, req.ContentType, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	return fileMetaPOToProto(meta), nil
+}
+
+// MoveFile moves a file from one folder to another.
+func (s *FileService) MoveFile(ctx context.Context, req *pb.MoveFileRequest) (*emptypb.Empty, error) {
+	err := s.folderUC.MoveFile(ctx, req.Id, req.TargetFolderId, req.OwnerId)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// --- Share operations ---
+
+// CreateShare creates a new share link for a resource.
+func (s *FileService) CreateShare(ctx context.Context, req *pb.CreateShareRequest) (*pb.ShareLink, error) {
+	var expiresAt *time.Time
+	if req.ExpiresAt != "" {
+		t, err := time.Parse(time.RFC3339, req.ExpiresAt)
+		if err != nil {
+			return nil, err
+		}
+		expiresAt = &t
+	}
+	var maxDownloads *int
+	if req.MaxDownloads > 0 {
+		md := int(req.MaxDownloads)
+		maxDownloads = &md
+	}
+
+	share, err := s.shareUC.CreateShare(ctx, req.ResourceType, req.ResourceId, req.Password, expiresAt, maxDownloads, req.CreatedBy)
+	if err != nil {
+		return nil, err
+	}
+	return shareLinkPOToProto(share), nil
+}
+
+// DeleteShare removes a share link.
+func (s *FileService) DeleteShare(ctx context.Context, req *pb.DeleteShareRequest) (*emptypb.Empty, error) {
+	err := s.shareUC.DeleteShare(ctx, req.Id, req.CreatedBy)
+	if err != nil {
+		return nil, err
+	}
+	return &emptypb.Empty{}, nil
+}
+
+// GetShareInfo returns share details and associated file metadata.
+func (s *FileService) GetShareInfo(ctx context.Context, req *pb.GetShareInfoRequest) (*pb.ShareInfo, error) {
+	share, fileMeta, err := s.shareUC.GetShareInfo(ctx, req.Token)
+	if err != nil {
+		return nil, err
+	}
+	if share == nil {
+		return nil, nil
+	}
+
+	info := &pb.ShareInfo{
+		Token:        share.Token,
+		ResourceType: share.ResourceType,
+		HasPassword:  share.Password != nil,
+	}
+	if share.ExpiresAt != nil {
+		info.ExpiresAt = share.ExpiresAt.Format(time.RFC3339)
+	}
+	if fileMeta != nil {
+		info.FileName = fileMeta.Name
+		info.FileSize = fileMeta.Size
+	}
+	return info, nil
+}
+
+// DownloadShare validates a share link and returns a presigned download URL.
+func (s *FileService) DownloadShare(ctx context.Context, req *pb.DownloadShareRequest) (*pb.DownloadShareResponse, error) {
+	url, fileName, err := s.shareUC.DownloadShare(ctx, req.Token)
+	if err != nil {
+		return nil, err
+	}
+	return &pb.DownloadShareResponse{
+		PresignedUrl: url,
+		FileName:     fileName,
+	}, nil
+}
+
+// --- Conversion helpers ---
+
+// folderPOToProto converts a data.FolderPO to a proto Folder message.
+func folderPOToProto(f *data.FolderPO) *pb.Folder {
+	if f == nil {
+		return nil
+	}
+	return &pb.Folder{
+		Id:        f.ID,
+		ParentId:  derefStr(f.ParentID),
+		Name:      f.Name,
+		OwnerId:   f.OwnerID,
+		CreatedAt: f.CreatedAt.Format(time.RFC3339),
+		UpdatedAt: f.UpdatedAt.Format(time.RFC3339),
+	}
+}
+
+// fileMetaPOToProto converts a data.FileMetaPO to a proto FileMeta message.
+func fileMetaPOToProto(f *data.FileMetaPO) *pb.FileMeta {
+	if f == nil {
+		return nil
+	}
+	return &pb.FileMeta{
+		Id:          f.ID,
+		FolderId:    f.FolderID,
+		Name:        f.Name,
+		S3Key:       f.S3Key,
+		S3Bucket:    f.S3Bucket,
+		Size:        f.Size,
+		ContentType: f.ContentType,
+		OwnerId:     f.OwnerID,
+		CreatedAt:   f.CreatedAt.Format(time.RFC3339),
+		UpdatedAt:   f.UpdatedAt.Format(time.RFC3339),
+	}
+}
+
+// shareLinkPOToProto converts a data.ShareLinkPO to a proto ShareLink message.
+func shareLinkPOToProto(s *data.ShareLinkPO) *pb.ShareLink {
+	if s == nil {
+		return nil
+	}
+	return &pb.ShareLink{
+		Id:            s.ID,
+		ResourceType:  s.ResourceType,
+		ResourceId:    s.ResourceID,
+		Token:         s.Token,
+		Password:      derefStr(s.Password),
+		ExpiresAt:     derefTime(s.ExpiresAt),
+		DownloadCount: int32(s.DownloadCount),
+		MaxDownloads:  derefInt(s.MaxDownloads),
+		CreatedBy:     s.CreatedBy,
+		CreatedAt:     s.CreatedAt.Format(time.RFC3339),
+	}
+}
+
+// derefStr returns the dereferenced string value or empty string if nil.
+func derefStr(s *string) string {
+	if s == nil {
+		return ""
+	}
+	return *s
+}
+
+// derefTime returns the formatted time string or empty string if nil.
+func derefTime(t *time.Time) string {
+	if t == nil {
+		return ""
+	}
+	return t.Format(time.RFC3339)
+}
+
+// derefInt returns the dereferenced int value as int32, or 0 if nil.
+func derefInt(i *int) int32 {
+	if i == nil {
+		return 0
+	}
+	return int32(*i)
+}
diff --git a/internal/service/service.go b/internal/service/service.go
new file mode 100644
index 0000000..6f10596
--- /dev/null
+++ b/internal/service/service.go
@@ -0,0 +1,6 @@
+package service
+
+import "github.com/google/wire"
+
+// ProviderSet is the Wire provider set for the service layer.
+var ProviderSet = wire.NewSet(NewFileService)