Abstract: Based on the PC+PMAC control mode, an open architecture control system of special arc-welding robot was developed for welding seam of intersection.The trinity logic control model of welding trajectory control, welding torch pose control and welding parameters control were put forward based on welding seam, which realized the real meaning of integrated control for welding robot movement and the welding power parameters.Two control methods of PPC and CDC were put forward and a hierarchical architecture of control system software was established, which realized the state detection of the welding process.The experimental results show that the control system has strong adaptability, good portability and can accomplish the welding of seam of intersection well.