diff --git a/transport/internet/kcp/config.go b/transport/internet/kcp/config.go
index 31844041..a7607cfb 100644
--- a/transport/internet/kcp/config.go
+++ b/transport/internet/kcp/config.go
@@ -1,10 +1,10 @@
 package kcp
 
 type Config struct {
-	Mtu              int // Maximum transmission unit
-	Tti              int
-	UplinkCapacity   int
-	DownlinkCapacity int
+	Mtu              uint32 // Maximum transmission unit
+	Tti              uint32
+	UplinkCapacity   uint32
+	DownlinkCapacity uint32
 	Congestion       bool
 	WriteBuffer      int
 }
@@ -13,11 +13,11 @@ func (this *Config) Apply() {
 	effectiveConfig = *this
 }
 
-func (this *Config) GetSendingWindowSize() int {
+func (this *Config) GetSendingWindowSize() uint32 {
 	return this.UplinkCapacity * 1024 * 1024 / this.Mtu / (1000 / this.Tti)
 }
 
-func (this *Config) GetReceivingWindowSize() int {
+func (this *Config) GetReceivingWindowSize() uint32 {
 	return this.DownlinkCapacity * 1024 * 1024 / this.Mtu / (1000 / this.Tti)
 }
 
diff --git a/transport/internet/kcp/config_json.go b/transport/internet/kcp/config_json.go
index c400078a..b476112a 100644
--- a/transport/internet/kcp/config_json.go
+++ b/transport/internet/kcp/config_json.go
@@ -11,11 +11,11 @@ import (
 
 func (this *Config) UnmarshalJSON(data []byte) error {
 	type JSONConfig struct {
-		Mtu        *int  `json:"mtu"`
-		Tti        *int  `json:"tti"`
-		UpCap      *int  `json:"uplinkCapacity"`
-		DownCap    *int  `json:"downlinkCapacity"`
-		Congestion *bool `json:"congestion"`
+		Mtu        *uint32 `json:"mtu"`
+		Tti        *uint32 `json:"tti"`
+		UpCap      *uint32 `json:"uplinkCapacity"`
+		DownCap    *uint32 `json:"downlinkCapacity"`
+		Congestion *bool   `json:"congestion"`
 	}
 	jsonConfig := new(JSONConfig)
 	if err := json.Unmarshal(data, &jsonConfig); err != nil {
@@ -39,7 +39,7 @@ func (this *Config) UnmarshalJSON(data []byte) error {
 	}
 	if jsonConfig.UpCap != nil {
 		upCap := *jsonConfig.UpCap
-		if upCap < 0 {
+		if upCap == 0 {
 			log.Error("KCP|Config: Invalid uplink capacity: ", upCap)
 			return common.ErrBadConfiguration
 		}
@@ -47,7 +47,7 @@ func (this *Config) UnmarshalJSON(data []byte) error {
 	}
 	if jsonConfig.DownCap != nil {
 		downCap := *jsonConfig.DownCap
-		if downCap < 0 {
+		if downCap == 0 {
 			log.Error("KCP|Config: Invalid downlink capacity: ", downCap)
 			return common.ErrBadConfiguration
 		}
diff --git a/transport/internet/kcp/connection.go b/transport/internet/kcp/connection.go
index 30cee644..64c5f1f1 100644
--- a/transport/internet/kcp/connection.go
+++ b/transport/internet/kcp/connection.go
@@ -20,7 +20,7 @@ var (
 )
 
 const (
-	headerSize = 2
+	headerSize uint32 = 2
 )
 
 type Command byte
@@ -65,7 +65,7 @@ type Connection struct {
 	writer          io.WriteCloser
 	since           int64
 	terminateOnce   signal.Once
-	writeBufferSize int
+	writeBufferSize uint32
 }
 
 // NewConnection create a new KCP connection between local and remote.
@@ -78,12 +78,11 @@ func NewConnection(conv uint32, writerCloser io.WriteCloser, local *net.UDPAddr,
 	conn.writer = writerCloser
 	conn.since = nowMillisec()
 
-	mtu := uint32(effectiveConfig.Mtu - block.HeaderSize() - headerSize)
-	conn.kcp = NewKCP(conv, mtu, conn.output)
-	conn.kcp.WndSize(effectiveConfig.GetSendingWindowSize(), effectiveConfig.GetReceivingWindowSize())
+	mtu := effectiveConfig.Mtu - uint32(block.HeaderSize()) - headerSize
+	conn.kcp = NewKCP(conv, mtu, effectiveConfig.GetSendingWindowSize(), effectiveConfig.GetReceivingWindowSize(), conn.output)
 	conn.kcp.NoDelay(effectiveConfig.Tti, 2, effectiveConfig.Congestion)
 	conn.kcp.current = conn.Elapsed()
-	conn.writeBufferSize = effectiveConfig.WriteBuffer / effectiveConfig.Mtu
+	conn.writeBufferSize = uint32(effectiveConfig.WriteBuffer) / effectiveConfig.Mtu
 
 	go conn.updateTask()
 
diff --git a/transport/internet/kcp/kcp.go b/transport/internet/kcp/kcp.go
index 662245f4..124be025 100644
--- a/transport/internet/kcp/kcp.go
+++ b/transport/internet/kcp/kcp.go
@@ -149,7 +149,7 @@ type KCP struct {
 	snd_queue []*Segment
 	rcv_queue []*Segment
 	snd_buf   []*Segment
-	rcv_buf   []*Segment
+	rcv_buf   *ReceivingWindow
 
 	acklist []uint32
 
@@ -161,11 +161,11 @@ type KCP struct {
 
 // NewKCP create a new kcp control object, 'conv' must equal in two endpoint
 // from the same connection.
-func NewKCP(conv uint32, mtu uint32, output Output) *KCP {
+func NewKCP(conv uint32, mtu uint32, sendingWindowSize uint32, receivingWindowSize uint32, output Output) *KCP {
 	kcp := new(KCP)
 	kcp.conv = conv
-	kcp.snd_wnd = IKCP_WND_SND
-	kcp.rcv_wnd = IKCP_WND_RCV
+	kcp.snd_wnd = sendingWindowSize
+	kcp.rcv_wnd = receivingWindowSize
 	kcp.rmt_wnd = IKCP_WND_RCV
 	kcp.mtu = mtu
 	kcp.mss = kcp.mtu - IKCP_OVERHEAD
@@ -176,6 +176,7 @@ func NewKCP(conv uint32, mtu uint32, output Output) *KCP {
 	kcp.ssthresh = IKCP_THRESH_INIT
 	kcp.dead_link = IKCP_DEADLINK
 	kcp.output = output
+	kcp.rcv_buf = NewReceivingWindow(receivingWindowSize)
 	return kcp
 }
 
@@ -205,19 +206,7 @@ func (kcp *KCP) Recv(buffer []byte) (n int) {
 	}
 	kcp.rcv_queue = kcp.rcv_queue[count:]
 
-	// move available data from rcv_buf -> rcv_queue
-	count = 0
-	for _, seg := range kcp.rcv_buf {
-		if seg.sn == kcp.rcv_nxt && len(kcp.rcv_queue) < int(kcp.rcv_wnd) {
-			kcp.rcv_queue = append(kcp.rcv_queue, seg)
-			kcp.rcv_nxt++
-			count++
-		} else {
-			break
-		}
-	}
-	kcp.rcv_buf = kcp.rcv_buf[count:]
-
+	kcp.DumpReceivingBuf()
 	// fast recover
 	if len(kcp.rcv_queue) < int(kcp.rcv_wnd) && fast_recover {
 		// ready to send back IKCP_CMD_WINS in ikcp_flush
@@ -227,6 +216,20 @@ func (kcp *KCP) Recv(buffer []byte) (n int) {
 	return
 }
 
+// DumpReceivingBuf moves available data from rcv_buf -> rcv_queue
+// @Private
+func (kcp *KCP) DumpReceivingBuf() {
+	for {
+		seg := kcp.rcv_buf.RemoveFirst()
+		if seg == nil {
+			break
+		}
+		kcp.rcv_queue = append(kcp.rcv_queue, seg)
+		kcp.rcv_buf.Advance()
+		kcp.rcv_nxt++
+	}
+}
+
 // Send is user/upper level send, returns below zero for error
 func (kcp *KCP) Send(buffer []byte) int {
 	var count int
@@ -357,43 +360,12 @@ func (kcp *KCP) parse_data(newseg *Segment) {
 		return
 	}
 
-	n := len(kcp.rcv_buf) - 1
-	insert_idx := 0
-	repeat := false
-	for i := n; i >= 0; i-- {
-		seg := kcp.rcv_buf[i]
-		if seg.sn == sn {
-			repeat = true
-			break
-		}
-		if _itimediff(sn, seg.sn) > 0 {
-			insert_idx = i + 1
-			break
-		}
+	idx := sn - kcp.rcv_nxt
+	if !kcp.rcv_buf.Set(idx, newseg) {
+		newseg.Release()
 	}
 
-	if !repeat {
-		if insert_idx == n+1 {
-			kcp.rcv_buf = append(kcp.rcv_buf, newseg)
-		} else {
-			kcp.rcv_buf = append(kcp.rcv_buf, &Segment{})
-			copy(kcp.rcv_buf[insert_idx+1:], kcp.rcv_buf[insert_idx:])
-			kcp.rcv_buf[insert_idx] = newseg
-		}
-	}
-
-	// move available data from rcv_buf -> rcv_queue
-	count := 0
-	for k, seg := range kcp.rcv_buf {
-		if seg.sn == kcp.rcv_nxt && len(kcp.rcv_queue) < int(kcp.rcv_wnd) {
-			kcp.rcv_queue = append(kcp.rcv_queue, kcp.rcv_buf[k])
-			kcp.rcv_nxt++
-			count++
-		} else {
-			break
-		}
-	}
-	kcp.rcv_buf = kcp.rcv_buf[count:]
+	kcp.DumpReceivingBuf()
 }
 
 // Input when you received a low level packet (eg. UDP packet), call it
@@ -790,15 +762,9 @@ func (kcp *KCP) Check(current uint32) uint32 {
 // interval: internal update timer interval in millisec, default is 100ms
 // resend: 0:disable fast resend(default), 1:enable fast resend
 // nc: 0:normal congestion control(default), 1:disable congestion control
-func (kcp *KCP) NoDelay(interval, resend int, congestionControl bool) int {
-	if interval >= 0 {
-		if interval > 5000 {
-			interval = 5000
-		} else if interval < 10 {
-			interval = 10
-		}
-		kcp.interval = uint32(interval)
-	}
+func (kcp *KCP) NoDelay(interval uint32, resend int, congestionControl bool) int {
+	kcp.interval = interval
+
 	if resend >= 0 {
 		kcp.fastresend = int32(resend)
 	}
@@ -806,20 +772,9 @@ func (kcp *KCP) NoDelay(interval, resend int, congestionControl bool) int {
 	return 0
 }
 
-// WndSize sets maximum window size: sndwnd=32, rcvwnd=32 by default
-func (kcp *KCP) WndSize(sndwnd, rcvwnd int) int {
-	if sndwnd > 0 {
-		kcp.snd_wnd = uint32(sndwnd)
-	}
-	if rcvwnd > 0 {
-		kcp.rcv_wnd = uint32(rcvwnd)
-	}
-	return 0
-}
-
 // WaitSnd gets how many packet is waiting to be sent
-func (kcp *KCP) WaitSnd() int {
-	return len(kcp.snd_buf) + len(kcp.snd_queue)
+func (kcp *KCP) WaitSnd() uint32 {
+	return uint32(len(kcp.snd_buf) + len(kcp.snd_queue))
 }
 
 func (this *KCP) ClearSendQueue() {
diff --git a/transport/internet/kcp/receiving.go b/transport/internet/kcp/receiving.go
new file mode 100644
index 00000000..f3bbc8c7
--- /dev/null
+++ b/transport/internet/kcp/receiving.go
@@ -0,0 +1,53 @@
+package kcp
+
+type ReceivingWindow struct {
+	start uint32
+	size  uint32
+	list  []*Segment
+}
+
+func NewReceivingWindow(size uint32) *ReceivingWindow {
+	return &ReceivingWindow{
+		start: 0,
+		size:  size,
+		list:  make([]*Segment, size),
+	}
+}
+
+func (this *ReceivingWindow) Size() uint32 {
+	return this.size
+}
+
+func (this *ReceivingWindow) Position(idx uint32) uint32 {
+	return (idx + this.start) % this.size
+}
+
+func (this *ReceivingWindow) Set(idx uint32, value *Segment) bool {
+	pos := this.Position(idx)
+	if this.list[pos] != nil {
+		return false
+	}
+	this.list[pos] = value
+	return true
+}
+
+func (this *ReceivingWindow) Remove(idx uint32) *Segment {
+	pos := this.Position(idx)
+	if this.list[pos] == nil {
+		return nil
+	}
+	e := this.list[pos]
+	this.list[pos] = nil
+	return e
+}
+
+func (this *ReceivingWindow) RemoveFirst() *Segment {
+	return this.Remove(0)
+}
+
+func (this *ReceivingWindow) Advance() {
+	this.start++
+	if this.start == this.size {
+		this.start = 0
+	}
+}
diff --git a/transport/internet/kcp/receiving_test.go b/transport/internet/kcp/receiving_test.go
new file mode 100644
index 00000000..ef2a6e72
--- /dev/null
+++ b/transport/internet/kcp/receiving_test.go
@@ -0,0 +1,32 @@
+package kcp_test
+
+import (
+	"testing"
+
+	"github.com/v2ray/v2ray-core/testing/assert"
+	. "github.com/v2ray/v2ray-core/transport/internet/kcp"
+)
+
+func TestRecivingWindow(t *testing.T) {
+	assert := assert.On(t)
+
+	window := NewReceivingWindow(3)
+
+	seg0 := &Segment{}
+	seg1 := &Segment{}
+	seg2 := &Segment{}
+	seg3 := &Segment{}
+
+	assert.Bool(window.Set(0, seg0)).IsTrue()
+	assert.Pointer(window.RemoveFirst()).Equals(seg0)
+
+	assert.Bool(window.Set(1, seg1)).IsTrue()
+	assert.Bool(window.Set(2, seg2)).IsTrue()
+
+	window.Advance()
+	assert.Bool(window.Set(2, seg3)).IsTrue()
+
+	assert.Pointer(window.RemoveFirst()).Equals(seg1)
+	assert.Pointer(window.Remove(1)).Equals(seg2)
+	assert.Pointer(window.Remove(2)).Equals(seg3)
+}