Pin boss welding process usually introduces side plate distortion of the hook, which leads to big assemble problem. Vibration stress release (VSR) method is introduced and used to reduce welding residual stress and control distortion of side plate. The VSR was studied experimentally firstly from theoretical analysis of the mechanism of stress strain and dislocation moving. The experimental results show that compared with untreated part, the distortion of VSR side plate is reduced by 66.9%, which meets assembly requirements of side plate. And there is no internal defect is introduced by the detection of ultrasonic flaw detector for weld seam of the side plate.