To investigate the rainfall-induce the seepage field of a high slope and effect factors, the theory of saturated-unsaturated infiltration was employed, and the numerical model of slope infiltration subjected to the rainfall are developed and programmed. The numerical results shown that, (1) With the increasing of the rainfall duration, rainfall water infiltration formed a transient saturated zone at slope surface, when the moist frontal surface reached to the groundwater level, the rainfall water would supply the groundwater. (2) Each effect factors on the seepage field play a strongest roles on the slope toe, weaker role on the middle part slope and weakest role on the top slope. (3) The longer rainfall duration, the deeper of infiltration depth. It also be deeper with the larger rainfall intensity, coefficient of permeability, the initial moisture content of the surface and the surface waterlogging depth. (4) The effect on seepage field would be faintly and could be ignored when the rainfall intensity was greater than 65.9mm/h and the surface waterlogging depth is greater than 0.3m. All above could provide technical ideas for analyzing slope seepage field under rainfall and accumulate fundamental data for early warning and preventing mud-rock flow and landslide.