Abstract: A servo gun spot welding control system was designed based on PLC controller.The system was integrated by servo gun,welding controller and other devices.During spot welding process,the electrode orientation was controlled by position loop of the servo motor;the electrode pressure was controlled according to the feedback pressure signal acquired by the load cell force sensor installed on the electrode;the communication with welding controller was accomplished by the I/O module of the system.Finally,experimental results are presented to demonstrate that the electrode orientation is quickly,and the welding pressure is very stable.It is also proved that servo gun can efficiently improve the welding quality,and reduce welding expulsion,and extend electrode life.