The seepage characteristics of gate dam have become one of the important factors influencing its safety and normal operation. To reduce the leakage flow rate of dam abutment and improve the seepage stability of dam foundation, engineering design of impervious curtain and cutoff wall has been developed. Through establishing a deep site for a hydropower station by the overall three-dimensional seepage field analysis, the rationality of the seepage control measures for the dam body is evaluated and the possibility of optimization is demonstrated. The results of the study demonstrate that the seepage control effect of the impervious system is remarkable and the cutoff scheme is reasonable and effective. The cutoff wall extends to a certain length and depth, thereby having a significant effect on reducing the seepage stability of dam abutment and dam foundation as well as improving the seepage stability of the overburden layer.