In order to provide the basis for dam seepage treatment, this paper quantitatively evaluated the abutment seepage of a reservoir dam. Visual MODFLOW was applied to simulate the change of groundwater flow field around the reservoir dam site.Meanwhile, the seepage flows before the impoundment of reservoir and after the impoundment of the reservoir at dam site section are both calculated. Simulation results show that because of the construction of dam, the surface water table rises up, which reverses the direction of groundwater flow.The amount of leakage at the section of dam site also has great growth. The dam has produced obvious effect on the regional groundwater environment. Hence,from the consideration of engineering safety, it is necessary to carry out some measures to protect the dam.