Abstract: This paper analysed the geology investigation data of left bank, and calculated stability coefficient under nature, seismic conditions and with crack hydrostatic pressure. By calculation, conclusion was gotten that with normal water storage, under condition of VII degree earthquake or high crack hydrostatic pressure, the left bank slope may be unstable. Then, advices were put forward that treatment measures should be adopted, such as water diversion, support, pressure relief and concrete anti-slide pile.