The　welding　seam　of　intersected　pipes　is　a　typical　and　complicated　space　welding　seam.　The　models　of　weld　position　and　welding　torch　pose　were　founded　for　arc　welding　robot,　and　their　position　and　pose　were　described　precisely　and　quantificationally　by　coordinates.　Then,　the　welding　torch　orientations　were　described　by　work　angle,　traveling　angle　and　rotation　angle,　and　the　calculation　methods　were　presented.　A　new　simple　method　of　calculation　is　put　forward　to　establish　the　coordinate　system　of　welding　seam　according　to　the　characteristic　analysis　that　any　tangent　through　the　point　on　intersection　line　coincides　with　the　intersection　line　of　two　cylinder　sections　at　this　point.　The　model　is　general　to　the　intersected　pipes　and　it　has　significance　for　modeling　on　weld　position　and　welding　torch　pose,　simulating　and　off　line　programming　for　robot　welding.