Abstract: Based on the coupling SPH and FEM method and the velocity weakening model of frictional strength of sliding surface, a numerical simulation method is developed which can reproduce the whole process of landslide from initial stable state, unstable state to sliding failure state. The constitutive model and the velocity weakening model adopted are simple in mathematical expression and the material parameters are easy to determined. From the analysis，the following results are obtained. (1) The numerical simulation of Tangjiashan landslide induced by earthquake is carried out, which reproduced the development of displacement and velocity of landslide mass, and the frictional strength on slide surface. The comparison between the simulation results and the on-site investigation or laboratory test results shows good consistency, which testified that the numerical method can reproduce the triggering and sliding process of the landslide. (2) Based on the calculated friction coefficient on the sliding surface, the landslide process is divided into four stages as follows: triggering stage, frictional weakening stage, low frictional stage and gradually stabilizing stage. In the moving process of the sliding mass, with the increase of velocity, the friction coefficient on the slide surface would decreases gradually. Therefore, high-speed movement of the sliding mass would be triggered by the interaction of the increase of velocity and the decrease of friction strength. (3) The parameter R defined by the ratio between the dynamic frictional force fd and dynamic sliding force Td is suggested as an indicator 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 position of the sliding surface, the process of friction weakening of the slide surface and the gradual failure of the landslide is revealed. The triggering of large landslide is due to the joint action of earthquake and the velocity weakening effect of frictional strength on sliding surface.