Abstract: Anti-seepage membrane(HDPE geomembrane) is widely used in anti-seepage projects currently that mainly prevent pollution, leakage and diffusion, and its laying form was various. In an underground water cutoff curtain project of an open-pit coal mine in China, the anti-seepage membrane was laid vertically as the main body of the water cutoff curtain wall, and the largest concealed depth was about 50 m. The different groove sections was overlapping connected by using connection box technology. Through the grouting and backfilling process, the impermeability of the curtain wall was improved and the anti-seepage membrane was compacted. Finally, pumping test in the surrounding wells was used to verify the impermeability of the curtain wall. The results showed that the permeability coefficient of anti-seepage membrane curtain wall was just 8.6×10^-7 cm/s which met the design requirements. The anti-seepage membrane curtain wall has the advantages of high efficiency, low cost, and environmental protection. The successful application of the anti-seepage membrane in this project has significant reference for other similar projects.