The laser shocking processing of AZ31B magnesium alloy sheet by the femtosecond laser pulse is numerically simulated with the finite element method. In the simulation, the effect of laser shock processing on the deformation process of AZ31B magnesium alloy is studied, the distributions of characteristics within the material, such as displacement, stress and strain, are analyzed, and the dynamic variation process of velocity and strain rate is discussed. The results indicate that the plastic deformation of magnesium alloy sheet shocked by single femtosecond laser pulse led to a micrometer-scale pit on the material surface. The maximum displacement at the center of the pit is 34 μm. And the maximum speed reaches 390m/s. Stress and strain of material aremainly distributed near the central dot and the edge of laser shocked region. The maximum stress of the central dot is 955 MPa, and the maximum strain rate reaches 1.8×106 s－1.The results show that the numerical simulation of the laser shocking processing of AZ31B magnesium alloy sheet by the femtosecond laser pulse is able to provide the numerical references for analysis of the variation laws of materials by femtosecond laser loading.