Welding is an important material processing method and widely used in industry. With the development of technology and the realization of the welding process, the required weld quality is higher and higher; applying the robot to the welding process is a revolutionary development, which totally changes the typical mode of rigid atomization to the flexible mode. Welding robot are made up of robot, robot controller and welding power and other equipments, it is stable and can enhance welding quality greatly, so it is a important application area for industrial robots. In this paper, the kinematics model of mobile welding robot was established and a sliding mode controller was designed, by Lyapnouv theory the stability was proved. The simulation shows the control performance and chattering reduction effect.