Abstract: In the paper, the liquefiable sand soil non-improved and improved by gravel piles under earthquake action is numerically simulated by using the three-dimensional finite difference program ‘FLAC3D’ (Fast Lagrangian Analysis of Continua), and a model to analyze seismic response is established in order to investigate the results of liquefiable sand soil reinforced by gravel piles. According to the analysis of the numerical simulation, the gravel piles confirmed have remarkable drainage effect. Compared with the result of shaking table tests, it is demonstrated that the test of Numerical simulation is reliable.