diff --git a/les/api.go b/les/api.go
index f9b8c34458..cd5c99a5f1 100644
--- a/les/api.go
+++ b/les/api.go
@@ -202,6 +202,18 @@ func (api *PrivateLightServerAPI) SetDefaultParams(params map[string]interface{}
 	return err
 }
 
+// SetConnectedBias set the connection bias, which is applied to already connected clients
+// So that already connected client won't be kicked out very soon and we can ensure all
+// connected clients can have enough time to request or sync some data.
+// When the input parameter `bias` < 0 (illegal), return error.
+func (api *PrivateLightServerAPI) SetConnectedBias(bias time.Duration) error {
+	if bias < time.Duration(0) {
+		return fmt.Errorf("bias illegal: %v less than 0", bias)
+	}
+	api.server.clientPool.setConnectedBias(bias)
+	return nil
+}
+
 // Benchmark runs a request performance benchmark with a given set of measurement setups
 // in multiple passes specified by passCount. The measurement time for each setup in each
 // pass is specified in milliseconds by length.
diff --git a/les/clientpool.go b/les/clientpool.go
index 8bcad95e15..05970f99ab 100644
--- a/les/clientpool.go
+++ b/les/clientpool.go
@@ -42,15 +42,7 @@ const (
 	persistCumulativeTimeRefresh = time.Minute * 5  // refresh period of the cumulative running time persistence
 	posBalanceCacheLimit         = 8192             // the maximum number of cached items in positive balance queue
 	negBalanceCacheLimit         = 8192             // the maximum number of cached items in negative balance queue
-
-	// connectedBias is applied to already connected clients So that
-	// already connected client won't be kicked out very soon and we
-	// can ensure all connected clients can have enough time to request
-	// or sync some data.
-	//
-	// todo(rjl493456442) make it configurable. It can be the option of
-	// free trial time!
-	connectedBias = time.Minute * 3
+	defaultConnectedBias         = time.Minute * 3  // the default connectedBias used in clientPool
 )
 
 // clientPool implements a client database that assigns a priority to each client
@@ -94,7 +86,7 @@ type clientPool struct {
 	freeClientCap     uint64         // The capacity value of each free client
 	startTime         mclock.AbsTime // The timestamp at which the clientpool started running
 	cumulativeTime    int64          // The cumulative running time of clientpool at the start point.
-	disableBias       bool           // Disable connection bias(used in testing)
+	connectedBias     time.Duration  // The connection bias. 0: Disable connection bias(used in testing)
 }
 
 // clientPoolPeer represents a client peer in the pool.
@@ -171,6 +163,7 @@ func newClientPool(db ethdb.Database, freeClientCap uint64, clock mclock.Clock,
 		startTime:      clock.Now(),
 		cumulativeTime: ndb.getCumulativeTime(),
 		stopCh:         make(chan struct{}),
+		connectedBias:  defaultConnectedBias,
 	}
 	// If the negative balance of free client is even lower than 1,
 	// delete this entry.
@@ -279,11 +272,7 @@ func (f *clientPool) connect(peer clientPoolPeer, capacity uint64) bool {
 			newCount--
 			return newCapacity > f.capLimit || newCount > f.connLimit
 		})
-		bias := connectedBias
-		if f.disableBias {
-			bias = 0
-		}
-		if newCapacity > f.capLimit || newCount > f.connLimit || (e.balanceTracker.estimatedPriority(now+mclock.AbsTime(bias), false)-kickPriority) > 0 {
+		if newCapacity > f.capLimit || newCount > f.connLimit || (e.balanceTracker.estimatedPriority(now+mclock.AbsTime(f.connectedBias), false)-kickPriority) > 0 {
 			for _, c := range kickList {
 				f.connectedQueue.Push(c)
 			}
@@ -371,6 +360,16 @@ func (f *clientPool) setDefaultFactors(posFactors, negFactors priceFactors) {
 	f.defaultNegFactors = negFactors
 }
 
+// setConnectedBias sets the connection bias, which is applied to already connected clients
+// So that already connected client won't be kicked out very soon and we can ensure all
+// connected clients can have enough time to request or sync some data.
+func (f *clientPool) setConnectedBias(bias time.Duration) {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+
+	f.connectedBias = bias
+}
+
 // dropClient removes a client from the connected queue and finalizes its balance.
 // If kick is true then it also initiates the disconnection.
 func (f *clientPool) dropClient(e *clientInfo, now mclock.AbsTime, kick bool) {
diff --git a/les/clientpool_test.go b/les/clientpool_test.go
index 6308113fe7..f8c4ef0c0c 100644
--- a/les/clientpool_test.go
+++ b/les/clientpool_test.go
@@ -91,7 +91,7 @@ func testClientPool(t *testing.T, connLimit, clientCount, paidCount int, randomD
 		}
 		pool = newClientPool(db, 1, &clock, disconnFn)
 	)
-	pool.disableBias = true
+	pool.setConnectedBias(0)
 	pool.setLimits(connLimit, uint64(connLimit))
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
@@ -248,7 +248,7 @@ func TestPaidClientKickedOut(t *testing.T) {
 		clock.Run(time.Millisecond)
 	}
 	clock.Run(time.Second)
-	clock.Run(connectedBias)
+	clock.Run(defaultConnectedBias)
 	if !pool.connect(poolTestPeer(11), 0) {
 		t.Fatalf("Free client should be accectped")
 	}