diff --git a/README.md b/README.md
index e952636..2743328 100644
--- a/README.md
+++ b/README.md
@@ -70,9 +70,14 @@ err := handler.Connect()
 defer handler.Close()
 
 client := modbus.NewClient(handler)
+client.ChangeSlaveId(0x02) //you  can change slaveId before use
 results, err := client.ReadDiscreteInputs(15, 2)
 ```
 
 References
 ----------
 -   [Modbus Specifications and Implementation Guides](http://www.modbus.org/specs.php)
+
+
+Update log：
+2017-07-12：add ChangeSlaveId api
\ No newline at end of file
diff --git a/api.go b/api.go
index fe06ab0..2a4c3f4 100644
--- a/api.go
+++ b/api.go
@@ -5,6 +5,7 @@
 package modbus
 
 type Client interface {
+	ChangeSlaveId(newSlaveId byte)	//add 2017-7-11
 	// Bit access
 
 	// ReadCoils reads from 1 to 2000 contiguous status of coils in a
diff --git a/asciiclient.go b/asciiclient.go
index 98d9c60..c3b11d0 100644
--- a/asciiclient.go
+++ b/asciiclient.go
@@ -46,6 +46,10 @@ type asciiPackager struct {
 	SlaveId byte
 }
 
+func (mb *asciiPackager) ChangeSlaveId(newSlaveId byte) {
+	mb.SlaveId = newSlaveId
+}
+
 // Encode encodes PDU in a ASCII frame:
 //  Start           : 1 char
 //  Address         : 2 chars
diff --git a/client.go b/client.go
index ac3ee2e..b9cec0a 100644
--- a/client.go
+++ b/client.go
@@ -20,6 +20,11 @@ type client struct {
 	transporter Transporter
 }
 
+//add 2017-7-11
+func (mb *client) ChangeSlaveId(newSlaveId byte) {
+	mb.packager.ChangeSlaveId(newSlaveId)
+}
+
 // NewClient creates a new modbus client with given backend handler.
 func NewClient(handler ClientHandler) Client {
 	return &client{packager: handler, transporter: handler}
diff --git a/modbus.go b/modbus.go
index 869473c..0ddc985 100644
--- a/modbus.go
+++ b/modbus.go
@@ -85,6 +85,7 @@ type Packager interface {
 	Encode(pdu *ProtocolDataUnit) (adu []byte, err error)
 	Decode(adu []byte) (pdu *ProtocolDataUnit, err error)
 	Verify(aduRequest []byte, aduResponse []byte) (err error)
+	ChangeSlaveId(newSlaveId byte)//add 2017-7-11
 }
 
 // Transporter specifies the transport layer.
diff --git a/rtuclient.go b/rtuclient.go
index ce55bd8..62ec970 100644
--- a/rtuclient.go
+++ b/rtuclient.go
@@ -42,6 +42,10 @@ type rtuPackager struct {
 	SlaveId byte
 }
 
+//add 2017-7-11
+func (mb *rtuPackager) ChangeSlaveId(newSlaveId byte) {
+	mb.SlaveId = newSlaveId
+}
 // Encode encodes PDU in a RTU frame:
 //  Slave Address   : 1 byte
 //  Function        : 1 byte
diff --git a/tcpclient.go b/tcpclient.go
index 4e53c73..8104bc6 100644
--- a/tcpclient.go
+++ b/tcpclient.go
@@ -55,6 +55,11 @@ type tcpPackager struct {
 	SlaveId byte
 }
 
+//add 2017-7-11
+func (mb *tcpPackager) ChangeSlaveId(newSlaveId byte) {
+	mb.SlaveId = newSlaveId
+}
+
 // Encode adds modbus application protocol header:
 //  Transaction identifier: 2 bytes
 //  Protocol identifier: 2 bytes