Abstract: On October 26, 2002, a floor water burst emerged in 21102 working face of Sanhejian Coal Mine. The source of water burst is Ordovician Karst water, the channel is hidden fault structure. In order to seal Ordovician Karst water in mine goaf, two lock walls located in roadways were built. There are some technical problems in the project. So following measures were taken: a. strengthening surrounding rock to prevent leakage; b. installing water pipe to low water temperature; c. optimizing concrete material, lowering water chemical heat, increasing concrete strength; d. self-making equipment for stirring and transport concrete to ensure continuous grouting. This project has been tested for more than one year, the result is excellent.