Abstract: When a seam is welded by robot, the torch may not be in best posture to weld due to the parts' geometric restriction. So it is necessary to previously analyze the relation between the tilting degree of torch and the lifting distance, for planning the torch's pose. This paper proposed a domain division method as a general and imaginable solution to such problem in robot welding of key components for rocket engine. Experiment and good result showed the proposed method can apply in off-line programming and previous planning for robot welding of many kinds of seam under geometric restriction.