A coupling between infiltration and ground surface overflow was studied in the condition of heavy rainfall (or atomized rain caused by the flood discharge) for the special geologic setting of Dayantang landslide,and the relationship between the intensity of rainfall and infiltration, overflow established. Then, on the basis of the unsaturated seepage theory, the seepage, stress, displacement and state security were analyzed during the rainfall by FEM, the safety factor of slope was calculated by the strength reduction. The base data on prevention and control works of the landslide are provided