The surface treatment of AM50 Mg alloys is conducted by the laser shock peening (LSP) technique. The resistance to tensile stress corrosion and the fracture morphologies of specimens in NaCl solution are investigated. The compositions of the fracture are also analyzed. The effects of laser shock layer number and Cl- concentration on the anticorrosion behavior of AM50 Mg alloys are researched. The results show that the large area LSP treatment to AM50 Mg alloys can induce the compressive residual stress and make the refinement of surface grains, and thus the resistance to tensile stress corrosion of AM50 Mg alloys is significantly improved. The resistance to tensile stress corrosion of AM50 Mg alloys is enhanced with the increase of laser shock layer number, but is weakened with the increase of Cl- concentration.