Abstract: Based on the systematic investigation of cha-shu-shan landslide on Chuan-Zang highway, this paper analyzes the landslide rock and soil structures,boundary conditions,deformation characteristics,influence factors and formation mechanism,and makes a in-depth discussions combined with 3DEC numerical simulation. The comprehensive analysis shows that the landslide is located in an active fault. The back edge rock is poor,and the front loose accumulation is thick. Under seismic activity,rainfall and other factors eliciting,the failure mechanism of landslide can be divided into the following 3 stages: (1)stage of toppling and pull-splitting,the back edge landslides stabilty is controled by the topography and structure of rock mass, where formes a rather strong dumped rupture deformation belt. Then generates slippage.(2)stage of creep deformation,the front loose accumulation body occurs creep deformation in a powerful gravity thrust.(3)stage of failing,clavicle segment are cutted in the weight thrust and the continuing effects of fault activity. Then the backedge potential slide plane and front shear slip plane are linked the whole landslide fails.