Reservoir water level fluctuations have grate influence on stability of bank slope after impounding and operation of the reservoir on Lancang River. Take a bank slope of the reservoir for example, according to the reservoir water level regulation and local hydrological data, the stability analysis of the bank slope was taken by using percolation theory and limit equilibrium methods. The change of the bank slope stability with its accumulations’ seepage was obtained base on simulation analysis of groundwater seepage field on the bank slope, and study on relationship between the change of pressure head and reservoir water level fluctuations, which has guidance function for evaluation and administration of reservoir bank slope.