Abstract: This paper presents a distributed control system for welding crossbeam structures. This system is developed to meet the task of crossbeam structure welding with two wires, double faces and multi-pass. It takes industrial PC as its host controller and several secondary controllers are connected to the host by computer bus. An bi-dimensional touch sensor with digital absolute encoder is developed to detect the warp of welding seam of workpiece. It uses AC motors and micro-step motors as executive units to complete the assistant motion such as installing, lefting, rotating of workpiece, to finish the automatic tracking of two weld guns along the welding seam, to improve the welding quality and efficiency, and to carry out automatic welding.