Abstract: When the 20MnSi controlled cooling bar is welded, there is a softened zone in the heat affect zone.The softened zone can diminish the load-bearing ability of the bar.By means of controlling the weld process variables and self-temper temperature, the weld-softening zone width can be controlled, and then the loadbearing ability can be improved.The relation model between the self-temper temperature and the welding parameters is gotten and analyzed by using the C.M.Adams formula.The results show that the weld-softening zone width decreases as the self-temper temperature increases, the weld-softening zone widens as the preheating temperature or the heat input increases, and the weld-softening zone of the smaller diameter of bar is wider than that of the bigger diameter of bar.