As the geomorphology of the studied reservoir bank presents typical mountainous and canyon characteristics, bending and ripping deformation of its slope occurs due to unloading and gravity, thus give rise to large scale landslide. The landslide may reactivate after impoundment of the reservior, hence may endanger the safety of the dam and other structures. Based on the environmental geological condition and the geological structure characteristics of the landslide, a geomechanics model has been established to simulate the forming process of the landslide. Finally, quantitative calculation method and numerical simulation method are used to compute landslide safety factor and stress distribution, etc. so as to further study and forecast the deformation and stability under impoundment, and provide basis for engineering design of the treatment.