Abstract: 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 analy sis 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.