Abstract: The concrete underground continuous wall has the advantages of convenient construction, reliable quality, good impermeability and so on. It is widely used in water conservancy, hydropower, foundation pit support, subway and other impermeability projects. The materials used are both plastic concrete and rigid concrete. In the water-cutting curtain project of an open-pit coal mine in Inner Mongolia, according to its engineering geological and hydrogeological characteristics, a kind of low-strength(8-10 MPa) impermeable(P6 grade) concrete was developed as the wall casting material, which water/cementitious materials ratio is 0.68, sand ratio is 45%, For 1 m³ of concrete, the content of each material is 180 kg of cement, 200 kg of fly ash, 20 kg of bentonite, 720 kg of sand and 880 kg of stones. The mechanism of permeability and anti-permeability was analyzed, and the results were verified by the test of drilling and pumping. The test results show that the concrete wall is complete and continuous, its compressive strength is up to 8.3 MPa, and its permeability coefficient is as low as 8.67×10^-7cm/s. After the implementation of the project, the drainage of the pit is significantly reduced, and the measure guarantees the development of safety, green and sustainable of coal mine, and has a significant economic, social and ecological benefit.