Abstract: The cause of crack defect of a shock absorber used in high-speed railway was analyzed. Through analysis, it is found that the welding crack defects of the shock absorber are mainly divided into two categories. The first category is the unfused defect and hardened crack caused by small heat input in the positioning and first pass welding. The second type is the crystalline crack caused by large heat input in the second pass welding. By improving the positioning welding parameters, that is, using a larg current of 240 A and long time swing welding, and using a smaller current of 200 A for the second pass weld immediately after the first pass welding, the welding defects of the shock absorber can be solved, which can provide reference for the welding of similar structural parts.