Abstract： A mobile welding robot was made, the kinematics and dynamics model of the welding mobile robot were established, and a control algorithm to achieve seam tracking of a mobile welding robot was proposed. Based on the dynamics of the mobile welding robot, the theories of sliding mode for robust control were used in the proposed control algorithm, and smooth continuous function was used instead of the traditional switching function to deduce the chattering. The effectiveness of the proposed method is verified by experiments. In the seam tracking process, the robot moves steadily without any obvious chattering.