In order to study the effect of laser shock processing (LSP) on mechanical properties of magnesium alloy, the room and thermal (300 ℃ ) tensile stress-strain curves of AZ31 alloy sheets are investigated by using electronic universal high temperature tensile machine and Nd: glass laser with wavelength of 1064 nm and pulse width of 20 ns. The results show that the room and thermal tensile strength of AZ31 alloy are improved by LSP. The maximum thermal flow stress of laser shocked specimens is obviously higher than that of untreated. However, the double- sided single LSP results in the reduction of mechanical properties at room temperature. And the spallation phenomenon which extends along subsurface occurs on fracture of the shocked samples. Effect of the residual compressive stress, mesostructures, surface morphologies and roughness on mechanical properties of magnesium alloy by LSP are discussed and analyzed.