diff --git a/api_file.go b/api_file.go
index 8450252..176370b 100644
--- a/api_file.go
+++ b/api_file.go
@@ -94,11 +94,12 @@ func (s *Service) HandleDownloadFile(
 	preview := req.QueryBool("preview")
 	newPath := utils.NormalizePath(path)
 
-	entry, downloader, err := s.FileSystemManager.DownloadFile(req.Context(), utils.FullPath(newPath))
+	downloader, entry, err := s.FileSystemManager.DownloadFile(req.Context(), utils.FullPath(newPath))
 	if err != nil {
 		logger.Error("download %s: %v", path, err)
 		return resp.InternalServerError("download file failed, " + err.Error())
 	}
+	defer downloader.Close()
 
 	if !preview {
 		resp.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%s", entry.FullPath.Name()))
diff --git a/engine/filesystem_manager.go b/engine/filesystem_manager.go
index 3fea3f4..4c2ed2c 100644
--- a/engine/filesystem_manager.go
+++ b/engine/filesystem_manager.go
@@ -158,7 +158,7 @@ func (f *FileSystemManager) CreateFile(ctx context.Context, path utils.FullPath,
 	return nil
 }
 
-func (f *FileSystemManager) DownloadFile(ctx context.Context, path utils.FullPath) (*utils.Entry, io.ReadSeeker, error) {
+func (f *FileSystemManager) DownloadFile(ctx context.Context, path utils.FullPath) (*utils.S3ReadSeeker, *utils.Entry, error) {
 	f.RLock()
 	defer f.RUnlock()
 
@@ -176,7 +176,7 @@ func (f *FileSystemManager) DownloadFile(ctx context.Context, path utils.FullPat
 		return nil, nil, fmt.Errorf("read s3 object failed: %v", err)
 	}
 
-	return entry, downloader, nil
+	return downloader, entry, nil
 }
 
 func (f *FileSystemManager) DeleteFile(ctx context.Context, path utils.FullPath, isDir bool) error {
diff --git a/engine/storage_manager.go b/engine/storage_manager.go
index 1353f81..296d7b7 100644
--- a/engine/storage_manager.go
+++ b/engine/storage_manager.go
@@ -121,7 +121,7 @@ func (sm *StorageManager) UploadFile(s3Key string, data io.Reader, contentType s
 	return output, nil
 }
 
-func (sm *StorageManager) DownloadFile(S3Key string) (io.ReadSeeker, error) {
+func (sm *StorageManager) DownloadFile(S3Key string) (*utils.S3ReadSeeker, error) {
 	head, err := sm.s3Client.HeadObject(&s3.HeadObjectInput{
 		Bucket: aws.String(sm.bucketName),
 		Key:    aws.String(S3Key),
diff --git a/utils/s3ReadSeeker.go b/utils/s3ReadSeeker.go
index 7fbff61..f10c4dc 100644
--- a/utils/s3ReadSeeker.go
+++ b/utils/s3ReadSeeker.go
@@ -8,6 +8,10 @@ import (
 	"github.com/aws/aws-sdk-go/service/s3"
 )
 
+const (
+	bufferSize = 4 * 1024 * 1024 // 4MB
+)
+
 type S3ReadSeeker struct {
 	client     *s3.S3
 	bucket     string
@@ -15,6 +19,9 @@ type S3ReadSeeker struct {
 	offset     int64
 	body       io.ReadCloser
 	contentLen int64
+	buffer     []byte
+	bufLen     int
+	bufPos     int
 }
 
 func NewS3ReadSeeker(client *s3.S3, bucket, key string, body io.ReadCloser, contentLen int64) *S3ReadSeeker {
@@ -24,22 +31,44 @@ func NewS3ReadSeeker(client *s3.S3, bucket, key string, body io.ReadCloser, cont
 		key:        key,
 		body:       body,
 		contentLen: contentLen,
+		buffer:     make([]byte, bufferSize),
 	}
 }
 
 func (r *S3ReadSeeker) Read(p []byte) (n int, err error) {
+	if r.bufPos < r.bufLen {
+		n = copy(p, r.buffer[r.bufPos:r.bufLen])
+		r.bufPos += n
+		return n, nil
+	}
+
 	if r.body == nil {
 		return 0, io.EOF
 	}
-	return r.body.Read(p)
+
+	if len(p) > bufferSize {
+		n, err = r.body.Read(p)
+		r.offset += int64(n)
+		return n, err
+	}
+
+	r.bufLen, err = r.body.Read(r.buffer)
+	if err != nil && err != io.EOF {
+		return 0, err
+	}
+
+	if r.bufLen > 0 {
+		r.bufPos = 0
+		n = copy(p, r.buffer[:r.bufLen])
+		r.bufPos = n
+		r.offset += int64(n)
+		return n, nil
+	}
+
+	return 0, io.EOF
 }
 
 func (r *S3ReadSeeker) Seek(offset int64, whence int) (int64, error) {
-	if r.body != nil {
-		r.body.Close()
-		r.body = nil
-	}
-
 	var newOffset int64
 	switch whence {
 	case io.SeekStart:
@@ -60,6 +89,19 @@ func (r *S3ReadSeeker) Seek(offset int64, whence int) (int64, error) {
 		return r.contentLen, nil
 	}
 
+	if newOffset >= r.offset-int64(r.bufLen) && newOffset < r.offset {
+		r.bufPos = int(newOffset - (r.offset - int64(r.bufLen)))
+		r.offset = newOffset
+		return newOffset, nil
+	}
+
+	if r.body != nil {
+		r.body.Close()
+		r.body = nil
+	}
+	r.bufLen = 0
+	r.bufPos = 0
+
 	result, err := r.client.GetObject(&s3.GetObjectInput{
 		Bucket: aws.String(r.bucket),
 		Key:    aws.String(r.key),