The anti-seepage project of large water storage tanks adopts HDPE geomembrane construction, with a membrane thickness of 1.5mm and a width of 6m. Before construction, the base should be leveled and sharp debris removed. Then, the geomembrane should be mechanically laid to ensure that the membrane surface is flat and free of wrinkles. The lap width should be controlled at 10-15 cm. The hot melt welding process is adopted. After welding, it is tested by inflation, and the sealing performance of the weld seam meets the standard at 100%. After the completion of the project, the anti-seepage effect of the reservoir was excellent. After the rainy season test, there was no leakage and it passed the acceptance smoothly.