Abstract: Based on the SPH-FEM coupling method, a frictional velocity weakening model for sliding surface is introduced and a numerical simulation method which can simulate the whole failure process of the landslides triggered by earthquake is proposed. The Tangjiashan landslide is simulated by the proposed method, and the simulated results are consistent with the on-site investigations and the laboratory test results. Based on the calculated frictional strength on the sliding surface, the whole failure process of the Tangjiashan landslide is divided into four stages: the triggering stage, the frictional weakening stage, the low frictional stage and the gradually stabilizing stage. The simulated results indicate that the high-speed movement of the sliding body is triggered by the interaction of the increase of the velocity and the decrease of the frictional strength. The parameter R defined by the ratio of the dynamic frictional force f_d to the dynamic sliding force T_d is suggested to evaluate the failure of large landslides. When R less than 1 occurs for the first time, the stress on the sliding surface reaches the shear strength and slope failure occurs. Based on the evolution of friction coefficient at different positions of the sliding surface, the frictional weakening of the sliding surface and the gradual failure of the landslide are revealed. The large-scale landslide is supposed to be triggered by the joint effects of the earthquake and the frictional velocity weakening.