Abstract: A new seam-tracking method based on dynamic trajectory planning for mobile welding robot is proposed in order to improve the response lag of the mobile robot and the high frequency oscillation in seam tracking. By using front-placed laser-based vision sensor to extract dynamically the location of weld seam in front of torch, the trend and direction of the weld line is roughly obtained. Than the robot system autonomously performs trajectory planning dynamically based on the isometric approximation model. Arc sensor technology is applied to detect the offset during welding process in real time. And the dynamic compensation of weld path is done in combination with the control of mobile robot and the executive body installed on it. Simulation and experiment results demonstrate that the method can effectively increase the stability of welding speed and smoothness of weld track and hence the weld forming in the curve and corner is improved.