<p>In order to reveal the evolution of the seepage field in the Baihetan Hydropower Station during the storage and operation periods, a simplified simulation method was proposed to simulate seven layers of drainage holes. The proposed method allows for diameter and spacing sensitivity analysis of drainage holes in a single simulation model. Entire- and sub-models were applied to reduce computational complexity and improve accuracy of finite element model, the entire-model can identify changes in sub-model boundary water levels due to the drainage system. The monitoring and calculation results show the pressure water head of the grouting tunnels and the flow rate of the drainage tunnels during the water storage period. For the underground powerhouses with large depth behind the dam, the design form of anti-seepage curtain and drainage system of Baihetan Hydropower Station can effectively reduce groundwater level and powerhouse flow rate. Groundwater level line was significantly lower through both the curtain and the drain hole curtain, which could ensure the safety of the powerhouse. Reducing the spacing between drainage holes or increasing their diameter further lowered groundwater levels. Reducing spacing had a more noticeable effect. This study is expected to provide a reference basis for the simulation of drainage holes, seepage field calculation, ati-seepange and drainage design of underground plant of hydropower station of similar projects.</p>