Laser Shock Processing (LSP) has become an advanced method for improving the mechanical properties such as hardness, residual stress and fatigue life. Nanosecond laser pulses of extreme intensity generated subsequent plasma. The rapid expansion of high pressure plasma creates a shock wave that propagates through the material, creating dislocations and inducing plastic deformation. Thus it can effectively eliminate welding residual tensile stress and improve fatigue capability of welding joints. The two kinds of welding experiment of 12Cr2Ni4A were designed to prove it. The experimental results showed that LSP has abroad application prospects in post-processing welding field.