Tonglusha copper mine is a large mine with underground and surface combined mining system. During the period of mining operation drainage and dewatering of the ore body caused a large area of surface subsidence and a great volume of surface water poured into underground space, posing serious threat to mining safely. Therefore it has been decided that curtian grout was used for sealing ground water and preventing subsidence. The project of curtian grout was completed on the basis of feasibility study and took four years and half. After completion of the project grout effectiveness was evaluated, 62% of sealing water rate was achieved, underground and surface drainage rate was reduced, water level difference between inside and outside of curtain become bigger (about 38m) , water level outside curtain has arisen and the surface subsidence was controled. The mine gained 40 M Yuan RMB of economical benefit as a result of the project.