diff --git a/client/image.go b/client/image.go
index 40dd1951..394ffd21 100644
--- a/client/image.go
+++ b/client/image.go
@@ -43,10 +43,10 @@ type imageUploadResponse struct {
 	IsExists      bool
 }
 
-func (c *QQClient) UploadImage(target message.Source, img io.ReadSeeker, thread ...int) (message.IMessageElement, error) {
+func (c *QQClient) UploadImage(target message.Source, img io.ReadSeeker) (message.IMessageElement, error) {
 	switch target.SourceType {
 	case message.SourceGroup, message.SourceGuildChannel, message.SourceGuildDirect:
-		return c.uploadGroupOrGuildImage(target, img, thread...)
+		return c.uploadGroupOrGuildImage(target, img)
 	case message.SourcePrivate:
 		return c.uploadPrivateImage(target.PrimaryID, img, 0)
 	default:
@@ -54,7 +54,7 @@ func (c *QQClient) UploadImage(target message.Source, img io.ReadSeeker, thread
 	}
 }
 
-func (c *QQClient) uploadGroupOrGuildImage(target message.Source, img io.ReadSeeker, thread ...int) (message.IMessageElement, error) {
+func (c *QQClient) uploadGroupOrGuildImage(target message.Source, img io.ReadSeeker) (message.IMessageElement, error) {
 	_, _ = img.Seek(0, io.SeekStart) // safe
 	fh, length := utils.ComputeMd5AndLength(img)
 	_, _ = img.Seek(0, io.SeekStart)
@@ -63,10 +63,6 @@ func (c *QQClient) uploadGroupOrGuildImage(target message.Source, img io.ReadSee
 	imgWaiter.Wait(key)
 	defer imgWaiter.Done(key)
 
-	tc := 1
-	if len(thread) > 0 {
-		tc = thread[0]
-	}
 	cmd := int32(2)
 	ext := EmptyBytes
 	if target.SourceType != message.SourceGroup { // guild
@@ -112,11 +108,7 @@ func (c *QQClient) uploadGroupOrGuildImage(target message.Source, img io.ReadSee
 		Ticket:    rsp.UploadKey,
 		Ext:       ext,
 	}
-	if tc > 1 && length > 3*1024*1024 {
-		_, err = c.highwaySession.UploadBDHMultiThread(input)
-	} else {
-		_, err = c.highwaySession.UploadBDH(input)
-	}
+	_, err = c.highwaySession.Upload(input)
 	if err != nil {
 		return nil, errors.Wrap(err, "upload failed")
 	}
@@ -306,7 +298,7 @@ func (c *QQClient) uploadOcrImage(img io.Reader, size int32, sum []byte) (string
 		Uuid:       binary.GenUUID(r),
 	})
 
-	rsp, err := c.highwaySession.UploadBDH(highway.Transaction{
+	rsp, err := c.highwaySession.Upload(highway.Transaction{
 		CommandID: 76,
 		Body:      img,
 		Size:      int64(size),
diff --git a/client/internal/highway/bdh.go b/client/internal/highway/bdh.go
index cc9a21d2..ff6ca5e7 100644
--- a/client/internal/highway/bdh.go
+++ b/client/internal/highway/bdh.go
@@ -3,7 +3,6 @@ package highway
 import (
 	"crypto/md5"
 	"io"
-	"net"
 	"sync"
 	"sync/atomic"
 
@@ -36,29 +35,7 @@ func (bdh *Transaction) encrypt(key []byte) error {
 	return nil
 }
 
-func (s *Session) retry(upload func(s *Session, addr Addr, trans *Transaction) ([]byte, error), trans *Transaction) ([]byte, error) {
-	// try to find a available server
-	for _, addr := range s.SsoAddr {
-		r, err := upload(s, addr, trans)
-		if err == nil {
-			return r, nil
-		}
-		if _, ok := err.(net.Error); ok {
-			// try another server
-			// TODO: delete broken servers?
-			continue
-		}
-		return nil, err
-	}
-	return nil, errors.New("cannot found available server")
-}
-
-func (s *Session) UploadBDH(trans Transaction) ([]byte, error) {
-	// encrypt ext data
-	if err := trans.encrypt(s.SessionKey); err != nil {
-		return nil, err
-	}
-
+func (s *Session) uploadSingle(trans Transaction) ([]byte, error) {
 	pc, err := s.selectConn()
 	if err != nil {
 		return nil, err
@@ -66,7 +43,7 @@ func (s *Session) UploadBDH(trans Transaction) ([]byte, error) {
 	defer s.putIdleConn(pc)
 
 	reader := binary.NewNetworkReader(pc.conn)
-	const chunkSize = 256 * 1024
+	const chunkSize = 128 * 1024
 	var rspExt []byte
 	offset := 0
 	chunk := make([]byte, chunkSize)
@@ -105,7 +82,7 @@ func (s *Session) UploadBDH(trans Transaction) ([]byte, error) {
 		buffers := frame(head, chunk)
 		_, err = buffers.WriteTo(pc.conn)
 		if err != nil {
-			return nil, errors.Wrap(err, "write pc error")
+			return nil, errors.Wrap(err, "write conn error")
 		}
 		rspHead, err := readResponse(reader)
 		if err != nil {
@@ -124,18 +101,22 @@ func (s *Session) UploadBDH(trans Transaction) ([]byte, error) {
 	return rspExt, nil
 }
 
-func (s *Session) UploadBDHMultiThread(trans Transaction) ([]byte, error) {
-	// for small file and small thread count,
-	// use UploadBDH instead of UploadBDHMultiThread
-	if trans.Size < 1024*1024*3 {
-		return s.UploadBDH(trans)
-	}
-
+func (s *Session) Upload(trans Transaction) ([]byte, error) {
 	// encrypt ext data
 	if err := trans.encrypt(s.SessionKey); err != nil {
 		return nil, err
 	}
 
+	const maxThreadCount = 4
+	threadCount := int(trans.Size) / (3 * 512 * 1024) // 1 thread upload 1.5 MB
+	if threadCount > maxThreadCount {
+		threadCount = maxThreadCount
+	}
+	if threadCount < 2 {
+		// single thread upload
+		return s.uploadSingle(trans)
+	}
+
 	// pick a address
 	// TODO: pick smarter
 	pc, err := s.selectConn()
@@ -145,9 +126,7 @@ func (s *Session) UploadBDHMultiThread(trans Transaction) ([]byte, error) {
 	addr := pc.addr
 	s.putIdleConn(pc)
 
-	// TODO: use idle conn
 	const blockSize int64 = 256 * 1024
-	const threadCount = 4
 	var (
 		rspExt          []byte
 		completedThread uint32
@@ -163,11 +142,12 @@ func (s *Session) UploadBDHMultiThread(trans Transaction) ([]byte, error) {
 			cond.Signal()
 		}()
 
+		// todo: get from pool?
 		pc, err := s.connect(addr)
 		if err != nil {
 			return err
 		}
-		// defer s.putIdleConn(pc) // TODO: should we put back?
+		defer s.putIdleConn(pc)
 
 		reader := binary.NewNetworkReader(pc.conn)
 		chunk := make([]byte, blockSize)
@@ -176,7 +156,8 @@ func (s *Session) UploadBDHMultiThread(trans Transaction) ([]byte, error) {
 			off := offset
 			offset += blockSize
 			id++
-			if int64(id) == count { // last
+			last := int64(id) == count
+			if last { // last
 				for atomic.LoadUint32(&completedThread) != uint32(threadCount-1) {
 					cond.Wait()
 				}
@@ -228,7 +209,7 @@ func (s *Session) UploadBDHMultiThread(trans Transaction) ([]byte, error) {
 			if rspHead.ErrorCode != 0 {
 				return errors.Errorf("upload failed: %d", rspHead.ErrorCode)
 			}
-			if rspHead.RspExtendinfo != nil {
+			if last && rspHead.RspExtendinfo != nil {
 				rspExt = rspHead.RspExtendinfo
 			}
 		}
diff --git a/client/internal/highway/highway.go b/client/internal/highway/highway.go
index 8028e15c..7a390938 100644
--- a/client/internal/highway/highway.go
+++ b/client/internal/highway/highway.go
@@ -135,7 +135,7 @@ type persistConn struct {
 	ping int64 // echo ping
 }
 
-const maxIdleConn = 5
+const maxIdleConn = 7
 
 type idle struct {
 	pc   persistConn
@@ -207,6 +207,7 @@ func (s *Session) connect(addr Addr) (persistConn, error) {
 	if err != nil {
 		return persistConn{}, err
 	}
+	_ = conn.(*net.TCPConn).SetKeepAlive(true)
 
 	// close conn
 	runtime.SetFinalizer(conn, func(conn net.Conn) {
diff --git a/client/multimsg.go b/client/multimsg.go
index eba7270e..a2d86f82 100644
--- a/client/multimsg.go
+++ b/client/multimsg.go
@@ -313,7 +313,7 @@ func (builder *ForwardMessageBuilder) Main(m *message.ForwardMessage) *message.F
 		Sum:       bodyHash[:],
 		Size:      int64(len(body)),
 	}
-	_, err = c.highwaySession.UploadBDH(input)
+	_, err = c.highwaySession.Upload(input)
 	if err != nil {
 		return nil
 	}
diff --git a/client/ptt.go b/client/ptt.go
index aaa2bc98..95896164 100644
--- a/client/ptt.go
+++ b/client/ptt.go
@@ -73,7 +73,7 @@ func (c *QQClient) UploadVoice(target message.Source, voice io.ReadSeeker) (*mes
 		ext = c.buildGroupPttStoreBDHExt(target.PrimaryID, fh, int32(length), 0, int32(length))
 	}
 	// multi-thread upload is no need
-	rsp, err := c.highwaySession.UploadBDH(highway.Transaction{
+	rsp, err := c.highwaySession.Upload(highway.Transaction{
 		CommandID: cmd,
 		Body:      voice,
 		Sum:       fh,
@@ -121,8 +121,7 @@ func (c *QQClient) UploadVoice(target message.Source, voice io.ReadSeeker) (*mes
 }
 
 // UploadShortVideo 将视频和封面上传到服务器, 返回 message.ShortVideoElement 可直接发送
-// thread 上传线程数
-func (c *QQClient) UploadShortVideo(target message.Source, video, thumb io.ReadSeeker, thread int) (*message.ShortVideoElement, error) {
+func (c *QQClient) UploadShortVideo(target message.Source, video, thumb io.ReadSeeker) (*message.ShortVideoElement, error) {
 	thumbHash := md5.New()
 	thumbLen, _ := io.Copy(thumbHash, thumb)
 	thumbSum := thumbHash.Sum(nil)
@@ -168,11 +167,7 @@ func (c *QQClient) UploadShortVideo(target message.Source, video, thumb io.ReadS
 		Ext:       ext,
 		Encrypt:   true,
 	}
-	if thread > 1 {
-		hwRsp, err = c.highwaySession.UploadBDHMultiThread(input)
-	} else {
-		hwRsp, err = c.highwaySession.UploadBDH(input)
-	}
+	hwRsp, err = c.highwaySession.Upload(input)
 	if err != nil {
 		return nil, errors.Wrap(err, "upload video file error")
 	}
diff --git a/client/upload_file.go b/client/upload_file.go
index 4f7fbacf..d8a0fc72 100644
--- a/client/upload_file.go
+++ b/client/upload_file.go
@@ -147,7 +147,7 @@ func (c *QQClient) UploadFile(target message.Source, file *LocalFile) error {
 		if target.SourceType == message.SourcePrivate {
 			input.CommandID = 69
 		}
-		if _, err := c.highwaySession.UploadBDHMultiThread(input); err != nil {
+		if _, err := c.highwaySession.Upload(input); err != nil {
 			return errors.Wrap(err, "upload failed")
 		}
 	}