Abstract: A mobile welding robot based on rotating arc sensor for bending weld was introduced in this paper. Two middle wheels drove the robot, and two universal wheels were placed in front and the rear of the robot to balance the robot body. It not only enhances the quickness of the robot, but also decreases the difficulty of control. Two DC servomotors controlled the cross-slider. A rotating arc sensor was integrated into welding torch. The structure of sensor was compact and real-time. The connection block of the welding torch and cross-slider was the combination structure. A connection block with rotational joint was used when the angle of welding seam charged frequently or greatly. The robot' s structure was compact and agile, which can realize automatic welding of the planar bending weld and the planar fillet weld seam.