The minimum slope stability safety factor occurs at one moment during the process of earthquake

it is unsuitable to evaluate the anti-slide stability of the slope under seismic load using this value. In this paper the minimum mean safety factor is presented as the evaluating index. The 0.65 times of the maximum amplitude of vibration of the safety factor is taken as the mean amplitude of vibration to evaluate the change of the safety factor with the ground motion time history. The anti-slide stability of a rockfill dam is evaluated by using the minimum mean safety factor. The result is compared with the one of the quasi-static method.