Abstract: In this paper, a seam tracking control method of a welding mobile robot working in narrow space was studied.A kinematic model of the robot was built for tracking right-angle fillet seams. And based on the newton-euler method, the dynamic behaviors of the driving wheel, the mobile body and the cross slider of the robot were analyzed, and then the overall dynamic model of the robot was obtained. On the basis of a reasonable simplification of the overall dynamic model, a robust PI controller was proposed. The simulation was performed on software Matlab and experiments was carried out. The results show that the proposed controller can complete the scheduled task possessing a high tracking accuracy.