The water conveyance and power generation system of pumped storage power stations is generally buried deeply,and the three-dimensional seepage field distribution of the plant’s chamber group is complex due to external seepage in the water diversion system. Drainage measures are crucial in controlling the seepage field of water transmission and power generation system. Using the three-dimensional seepage field finite element method, we constructed a numerical calculation model of Zhangye pumped storage power station’s water delivery and power generation system, integrating the water conveyance system, underground plant system, and seepage prevention and drainage systems. Based on the distribution law of seepage field within the power generation system, we analyzed the impact of the drainage system beneath the pressure pipeline and the plant’s drainage system on the seepage field. Results indicate that under normal operating conditions, most of the underground plant is above the wetting line, and seepage flow is maintained within a reasonable range under the designed seepage control plan. Seepage overflows occur near the bottom of the plant chamber group, the pipeline exhibits characteristics of internal water seepage, and the seepage flow of the tailwater system is relatively large. The lower drainage gallery of the pressure pipe significantly influences the seepage field of the pressure pipe and the upstream side of the plant. A smaller drainage hole spacing results in a lower wetting line and larger seepage flow in the corresponding area, with a drainage hole spacing of 3 m proving more reasonable. The drainage system in the plant area significantly affects the seepage field of the underground plant. As the drainage hole spacing increases, the drainage effect diminishes, the flow into the collection well decreases, the wetting line rises slightly, and a drainage hole spacing of 3 m is deemed more reasonable.