Abstract: Investigation of the slopes in Wenchuan earthquake shows that tension failures mostly appear in the slope crests,and shear failure in slope toe. Beginning with the stress state of soil,using the finitedifference method,the failure process of slope is analyzed under the given conditions of static,horizontal and coupled earthquake by monitoring the changing of state,displacement,and shearstrain increment. The calculated results indicate that the slope crest is tensile damage and shear failure appears in slope toe. It is different from the traditional opinion of geological engineering that slope damage under earthquakes is mainly shear failure due to seismic inertia force. A new method of the relative displacement of key points is put out to judge the dynamic stability. Numerical simulation results have good consistency with existing research results and postseismic investigation findings．