Reservoir landslide is a severe geological hazard which is caused by the hydrodynamic change due to rainfall and fluctuation of reservoir level. The hydrodynamic change and its influence on landslide stability of Qianjiangping landslide before and after impoundment of the Three Gorges Reservoir are studied combining with its hydrogeological structure. There are two relatively independent hydrogeological units on both sides of the slipband. Before impoundment, the outlet of groundwater under slipband is above the river level, the supply and discharge of groundwater is in equilibrium, and the excess pore water pressure at the bottom of slipband is smaller or not exists. After impounding, the outlet of groundwater is under reservoir level and the discharge of groundwater is hindered, so the excess pore water pressure at the bottom of slipband will rises and the safety factor of the landslide will decreases. Combing with other factors, the stability of the landslide will further decreases and lead to landslide failure finally.
