Abstract: In order to study the influence of laser shock peening on the thermal stability property of A356 Al alloy, after laser shock peening A356 Al alloy workpieces with Nd:YAG laser and annealing them at 220℃ their microstructure, micro-hardness and residual stress were studied. A series of experimental data were got. The results showed that laser shock peening can effectively improve the thermal stability of A356 Al alloys. The large residual compressive stress was induced by laser shock peening on the surface, micro-hardness and the surface dislocation density was increased significantly; the grain was refined obviously. After annealing, the residual compressive stress was decreased by 30.68%, the dislocation density (full width at half maximum) was decreased from 1.63°to 1.51°, and the micro-hardness was decreased by 19.42%, the grain size on the surface layer was grown up slightly. However, compared to the matrix, the scale was less. The results were helpful to expand application fields of laser shock peening and A356 Al alloy.