For the welding of metal structures at certain space position,the position and posture of welding torch relative to the workpiece（welding groove） directly affect the weld forming quality. The optimal relative posture of welding torch is determined by the absolute spatial pose of the plane where the weld seam（joint） is located and the characteristic size parameters of welding groove. The research and application of vision sensing in welding field are analyzed briefly,and the common methods for the detection of the space posture of welding torch are summarized. On the basis,the combined detection system based on the fusion of vision and gravity sensing information is introduced,which can detect the absolute spatial posture of the plane where the weld seam（joint） is located,the relative position and posture of welding torch relative to this plane,and the characteristic size parameters of welding groove. Then,the detection and tracking of complex space weld seam（joint）in the plane whose posture is unknown and the posture control of welding torch are realized. In the end,the research and app-lication prospect of the combined detection system based on the fusion of vision and gravity sensing information in the welding of complex space seam（ joint） within spatial curved workpiece is given.