diff --git a/client/daemon/rpcserver/subscriber.go b/client/daemon/rpcserver/subscriber.go
index 4028a9dd0..a9382f7ad 100644
--- a/client/daemon/rpcserver/subscriber.go
+++ b/client/daemon/rpcserver/subscriber.go
@@ -115,9 +115,13 @@ func searchNextPieceNum(sentMap map[int32]struct{}, cur uint32) (nextPieceNum ui
 }
 
 // sendExistPieces will send as much as possible pieces
-func (s *subscriber) sendExistPieces(startNum uint32) (total int32, err error) {
+func (s *subscriber) sendExistPieces(startNum uint32) error {
 	s.request.StartNum = startNum
-	return sendExistPieces(s.sync.Context(), s.SugaredLoggerOnWith, s.getPieces, s.request, s.sync, s.sentMap, true)
+	total, err := sendExistPieces(s.sync.Context(), s.SugaredLoggerOnWith, s.getPieces, s.request, s.sync, s.sentMap, true)
+	if total > -1 && s.isUnknownTotalPieces() {
+		s.totalPieces = total
+	}
+	return err
 }
 
 func (s *subscriber) receiveRemainingPieceTaskRequests() {
@@ -161,9 +165,23 @@ func (s *subscriber) receiveRemainingPieceTaskRequests() {
 	}
 }
 
+// totalPieces is -1, 0, n
+func (s *subscriber) isKnownTotalPieces() bool {
+	return s.totalPieces > -1
+}
+
+func (s *subscriber) isUnknownTotalPieces() bool {
+	return !s.isKnownTotalPieces()
+}
+
+func (s *subscriber) isAllPiecesSent(nextPieceNum uint32) bool {
+	return nextPieceNum == uint32(s.totalPieces)
+}
+
 func (s *subscriber) sendRemainingPieceTasks() error {
 	// nextPieceNum is the least piece num which did not send to remote peer
-	// may great then total piece count, check the total piece count when use it
+	// available values: [0, n], n is total piece count
+	// when nextPieceNum is n, indicate all pieces done
 	var nextPieceNum uint32
 	s.Lock()
 	for i := int32(s.skipPieceCount); ; i++ {
@@ -173,6 +191,7 @@ func (s *subscriber) sendRemainingPieceTasks() error {
 		}
 	}
 	s.Unlock()
+	s.Debugf("desired next piece num: %d", nextPieceNum)
 loop:
 	for {
 		select {
@@ -182,51 +201,54 @@ loop:
 		case info := <-s.PieceInfoChannel:
 			s.Infof("receive piece info, num: %d, finished: %v", info.Num, info.Finished)
 			// not desired piece
-			if s.totalPieces > -1 && uint32(info.Num) < nextPieceNum {
+			if uint32(info.Num) < nextPieceNum {
 				continue
 			}
 
 			s.Lock()
-			total, err := s.sendExistPieces(uint32(info.Num))
+			err := s.sendExistPieces(uint32(info.Num))
 			if err != nil {
 				err = s.saveError(err)
 				s.Unlock()
 				return err
 			}
-			if total > -1 && s.totalPieces == -1 {
-				s.totalPieces = total
-			}
-			if s.totalPieces > -1 && len(s.sentMap)+int(s.skipPieceCount) == int(s.totalPieces) {
-				s.Unlock()
-				break loop
-			}
-			if info.Finished {
-				s.Unlock()
-				break loop
-			}
+
 			nextPieceNum = s.searchNextPieceNum(nextPieceNum)
+			s.Debugf("update desired next piece num: %d", nextPieceNum)
+
+			if info.Finished && s.isAllPiecesSent(nextPieceNum) {
+				s.Unlock()
+				break loop
+			}
 			s.Unlock()
 		case <-s.Success:
 			s.Infof("peer task is success, send remaining pieces")
 			s.Lock()
 			// all pieces already sent
 			// empty piece task will reach sendExistPieces to sync content length and piece count
-			if s.totalPieces > 0 && nextPieceNum == uint32(s.totalPieces) {
+			if s.totalPieces > 0 && s.isAllPiecesSent(nextPieceNum) {
 				s.Unlock()
 				break loop
 			}
-			total, err := s.sendExistPieces(nextPieceNum)
+
+			err := s.sendExistPieces(nextPieceNum)
 			if err != nil {
 				err = s.saveError(err)
 				s.Unlock()
 				return err
 			}
-			if total > -1 && s.totalPieces == -1 {
-				s.totalPieces = total
-			}
-			if s.totalPieces > -1 && len(s.sentMap)+int(s.skipPieceCount) != int(s.totalPieces) {
+
+			if s.isUnknownTotalPieces() {
 				s.Unlock()
-				msg := "peer task success, but can not send all pieces"
+				msg := "task success, but total pieces is unknown"
+				s.Errorf(msg)
+				return dferrors.Newf(commonv1.Code_ClientError, msg)
+			}
+
+			nextPieceNum = s.searchNextPieceNum(nextPieceNum)
+			if !s.isAllPiecesSent(nextPieceNum) {
+				s.Unlock()
+				msg := "task success, but not all pieces are sent out"
 				s.Errorf(msg)
 				return dferrors.Newf(commonv1.Code_ClientError, msg)
 			}