Abstract: Reservoir water level change can change the seepage field in the bank slope of the reservoir, and further cause the instability and failure of the slope. The seepage field in the slope can be divided in saturated and unsaturated seepage fields. The paper presents the calculated results of the position change of the underground water level line and the corresponding seepage field parameters. The results show that the rising velocity of the underground water level line in the bedrock evidently lags that in the upper loose deposit. This difference is due to the difference of the permeability coefficients between upper loose deposit and the base rock. The variation magnitudes of the seepage parameters such as the volume content, the pressure head, the flow velocity and the hydraulic gradient in the bedrock are rather smaller than those in the upper loose deposit. It indicates that the influence of the reservoir water level rise on the upper loose deposit is much more evident.