Surface modification of 800H high temperature alloy welded joint was carried out by laser shock strengthening process. The influence of microstructure evolution and residual stress on welded joint was studied, and numerical simulation of welding and laser shock was carried out by Abaqus. Results show that laser shock strengthening can significantly refine the grain size of welded joints. Impact strengthening can effectively improve the residual stress distribution near welded joint surface, and stress distribution changes from 165~216 MPa to -212~-98 MPa. The stress distribution trend after impact strengthening is basically consistent with the numerical analysis results. The numerical analysis results can provide reference for laser impact weldment.