The numerical simulation method of the saturated-unsaturated seepage flow is presented. The pore-water pressure is simulated under rainfall conditions adopted this program. The traditional method handled the rainfall infiltration boundary is conquered

and the real alteration of the rainfall infiltration boundary is taken into consideration to give a good basis for the coupling simulation of the saturated-unsaturated seepage flow and surface overflow. As a result this method is very suitable to the real rainfall process; so It is very helpful to analyzing the reason for rainfall-induced landslides.