Abstract: Welding is the key course in manufacturing the spherical valve core through steel tube's necking, assembling, welding and grinding.Because the necked workpiece is under stress before welding and is to be prepared for grinding after welding, how to choose sound welding parameters so as to control residual stress with the precondition of excellent weld quality becomes the focus of this paper.A series of numerical simulations which show the real-time dynamic changes under different welding parameters for necked workpiece are demonstrated, and the optimization parameters are obtained through comparing the welding size and residual stress after welding.Analysis and illustrations on the accumulated results show that the residual stress after welding is overlapped in the former procedures.