Abstract: The geomembrane is adopted for seepage-prevention in the upper reservoir bottom of Liyang Pumped Storage Power Plant. According to the principle of “upper closure and lower drainage and combination of water resistance and drainage”, the three-dimensional composite drainage net is set up below the geomembrane to collect and drain leaked water through the geomembrane in time. It is the first time to adopt so large area of three-dimensional composite drainage net in the hydropower project in China. The actual drainage effect and capacity should be tested after the impoundment and operation of the project.