Abstract：Based on the characteristics of collapse and landslide induced by Wenchuan earthquake that the quantity，the distribution density and the influential area，etc. are large，the damage mechanism of the complex structural slope is analyzed under strong earthquake，and the different stress-strain curves of some points in slope are given under microseism and strong earthquake. It is pointed that slope will generate additional stress under the effect of earthquake. The superposition of the additional stress and the original stress forms the total stress. When the total stress is larger than the tensile strength of the rock，tensile fracture occurs. The tensile fracture criterion is given. The finite element method is used to simulate tensile fracture process of slope with single weak plane under strong earthquake. The following conclusions can be drawn. When the first principal(tensile) stress is greater than or equal to tensile strength of rock，it cracks and can not bear tensile stress but compressive stress；if the total stress state meets the plastic yield criterion，shear failure occurs；the tensile fracture region cumulates continuously during earthquake dynamic，that is，the loose degree and the loose range become increase；and the slope containing weak plane can easily crack along the weak plane under earthquake.
