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.