In the field of robot flexible welding,a multi-robot master-slave coordinated motion control system is designed and implemented. The system adopts a centralized control architecture and a cyclic synchronous position mode.Based on a general multi-robot master-slave coordinated motion control algorithm,the coordinated motion target matrix of slave robot is calculated. Furthermore,the master-slave coordinated motion control process and the corresponding programming instruction set are designed in robot controller.Finally,a multi-robot flexible welding system is set up with four Kaierda KR1440 robots. Through the test of robot program teaching and playback for typical master-slave coordinated welding tasks,the multi-robot master-slave state online switch function is realized and the effectiveness of the control system is verified. This work provides a technical basis for further improving the flexibility of the robot welding system.