diff --git a/transport/internet/kcp/kcp.go b/transport/internet/kcp/kcp.go
index 4e23f972..f13df238 100644
--- a/transport/internet/kcp/kcp.go
+++ b/transport/internet/kcp/kcp.go
@@ -81,7 +81,7 @@ func NewKCP(conv uint16, mtu uint32, sendingWindowSize uint32, receivingWindowSi
 	kcp.rcv_buf = NewReceivingWindow(receivingWindowSize)
 	kcp.snd_queue = NewSendingQueue(sendingQueueSize)
 	kcp.rcv_queue = NewReceivingQueue()
-	kcp.acklist = new(ACKList)
+	kcp.acklist = NewACKList(kcp)
 	kcp.cwnd = kcp.snd_wnd
 	return kcp
 }
@@ -250,9 +250,7 @@ func (kcp *KCP) HandleReceivingNext(receivingNext uint32) {
 }
 
 func (kcp *KCP) HandleSendingNext(sendingNext uint32) {
-	if kcp.acklist.Clear(sendingNext) {
-		kcp.receivingUpdated = true
-	}
+	kcp.acklist.Clear(sendingNext)
 }
 
 func (kcp *KCP) parse_data(newseg *DataSegment) {
@@ -367,16 +365,9 @@ func (kcp *KCP) flush() {
 	lost := false
 
 	// flush acknowledges
-	//if kcp.receivingUpdated {
-	ackSeg := kcp.acklist.AsSegment()
-	if ackSeg != nil {
-		ackSeg.Conv = kcp.conv
-		ackSeg.ReceivingWindow = uint32(kcp.rcv_nxt + kcp.rcv_wnd)
-		ackSeg.ReceivingNext = kcp.rcv_nxt
-		kcp.output.Write(ackSeg)
+	if kcp.acklist.Flush() {
 		kcp.receivingUpdated = false
 	}
-	//}
 
 	// calculate window size
 	cwnd := kcp.snd_una + kcp.snd_wnd
diff --git a/transport/internet/kcp/receiving.go b/transport/internet/kcp/receiving.go
index 22c3c578..342712ea 100644
--- a/transport/internet/kcp/receiving.go
+++ b/transport/internet/kcp/receiving.go
@@ -149,22 +149,35 @@ func (this *ReceivingQueue) Close() {
 }
 
 type ACKList struct {
+	kcp        *KCP
 	timestamps []uint32
 	numbers    []uint32
+	nextFlush  []uint32
+}
+
+func NewACKList(kcp *KCP) *ACKList {
+	return &ACKList{
+		kcp:        kcp,
+		timestamps: make([]uint32, 0, 32),
+		numbers:    make([]uint32, 0, 32),
+		nextFlush:  make([]uint32, 0, 32),
+	}
 }
 
 func (this *ACKList) Add(number uint32, timestamp uint32) {
 	this.timestamps = append(this.timestamps, timestamp)
 	this.numbers = append(this.numbers, number)
+	this.nextFlush = append(this.nextFlush, 0)
 }
 
-func (this *ACKList) Clear(una uint32) bool {
+func (this *ACKList) Clear(una uint32) {
 	count := 0
 	for i := 0; i < len(this.numbers); i++ {
 		if this.numbers[i] >= una {
 			if i != count {
 				this.numbers[count] = this.numbers[i]
 				this.timestamps[count] = this.timestamps[i]
+				this.nextFlush[count] = this.nextFlush[i]
 			}
 			count++
 		}
@@ -172,26 +185,34 @@ func (this *ACKList) Clear(una uint32) bool {
 	if count < len(this.numbers) {
 		this.numbers = this.numbers[:count]
 		this.timestamps = this.timestamps[:count]
-		return true
+		this.nextFlush = this.nextFlush[:count]
 	}
-	return false
 }
 
-func (this *ACKList) AsSegment() *ACKSegment {
-	count := len(this.numbers)
-	if count == 0 {
-		return nil
+func (this *ACKList) Flush() bool {
+	seg := &ACKSegment{
+		Conv:            this.kcp.conv,
+		ReceivingNext:   this.kcp.rcv_nxt,
+		ReceivingWindow: this.kcp.rcv_nxt + this.kcp.rcv_wnd,
 	}
-
-	if count > 128 {
-		count = 128
+	if this.kcp.state == StateReadyToClose {
+		seg.Opt = SegmentOptionClose
 	}
-	seg := &ACKSegment{
-		Count:         byte(count),
-		NumberList:    this.numbers[:count],
-		TimestampList: this.timestamps[:count],
+	current := this.kcp.current
+	for i := 0; i < len(this.numbers); i++ {
+		if this.nextFlush[i] <= current {
+			seg.Count++
+			seg.NumberList = append(seg.NumberList, this.numbers[i])
+			seg.TimestampList = append(seg.TimestampList, this.timestamps[i])
+			this.nextFlush[i] = current + 50
+			if seg.Count == 128 {
+				break
+			}
+		}
 	}
-	//this.numbers = nil
-	//this.timestamps = nil
-	return seg
+	if seg.Count > 0 {
+		this.kcp.output.Write(seg)
+		return true
+	}
+	return false
 }