The work aims to investigate the effects of laser shock peening on the microstructure and high temperature tensile properties of aluminized 321 stainless steel. The aluminizing was carried out to tensile sample of 321 austenitic stainless steel by packed cementation to prepare the aluminized steel. Then the double-side gauge area (8 mm′25 mm) of aluminized steel was performed by laser shock process with different parameters: pulse wave length of 1064 nm, pulse energy of 7 J, pulse width of 20 ns, circular spot diameter of 2.6~3 mm and overlapping ratio of 50%. Black tape was used as the protective layer and water was used as the restraint layer. The surface integrity of aluminized steel was evaluated and then high temperature tensile test was carried out to aluminized steel at 620 ℃ to obtain the true stress-true strain curve, the yield strength, ultimate strength and elongation. The fracture morphology was observed by scanning electron microscopy. The surface roughness and micro-hardness of aluminized steel increased with the increasing of laser power density and impact times. Aluminized steel processed by laser shock exhibited higher yield strength, tensile strength and elongation. The aluminized steel with laser energy density of 6.59 GW/cm2 and three-times of impact showed the best tensile performance. The high-temperature tensile fracture of aluminized steel strengthened by laser impact exhibited the ductile fracture characteristics. Obvious plastic deformation occurs at the surface of aluminized steel after laser shock, resulting in larger pit and boss and changing the material roughness. Refinement of surface grains, intensive dislocation and increase of dislocation improve the surface hardness and the depth of hardening impact layer by laser shock. In addition, the release of introduced high amplitude residual compressive stress can offset the external tension and delay the formation and extension of surface crack. Therefore, laser shock strengthening improves the mechanical properties of aluminized steel.