Abstract: With plenty of large mines and relatively deep buried coal seam,Yuheng mining area (north area) of Juras-sic coalfield in northern Shaanxi Province is an important coal production base in China. However,the water-rich coal seam also brings a lot of issues in the mining process,which are very rare both in China and the world. To study the water-rich mechanism of coal seam and the water hazards in the mining process,this paper takes the grouting and blocking water project of No. 2 water-rich coal seam of Balasu coal mine as an example. Based on the analysis of the hydro-geological conditions and the hydraulic relationship between the underground aquifers, this study ascertained the hydrogeological characteristics and types of each aquifer in the region,identified that No. 2 coal seam water was the main water source for the vertical shaft passing through the coal seam,then put forward a new security technology for water-rich coal seam grouting treatment for the first time. Through pumping test and hydrochemical test,it was found that the groundwater aquifers in the area mainly contain the Quaternary loose phreatic aquifer,the pore-fissure aquifer of lower Cretaceous Luohe formation,the clastic rock fissure aquifer of middle Jurassic Zhiluo formation,the clastic rock fissure aquifer of No. 2 coal seam roof Yan’an formation,and the No. 2 coal seam aquifer,etc. A close hydraulic relationship between the Quaternary loose phreatic aquifer and the Cretaceous Luohe formation pore-fissure aquifer was found,but no hydraulic relationship was found among other aquifers. After trying for many times,the sealing of No. 2 water-rich coal seam was successfully completed with the general idea of “drainage grouting,curtain sealing” and the methods of “drilling underground,slurry mixing on the ground,pipeline transportation and high-pressure perfusion”. The research shows that an effective water-stopping curtain can be formed around the exposed section of shaft inset coal seam and the roadway to be excavated in the auxiliary shaft through the combination of various materials and the implementation of drilling grouting technique. As a result,the drivage roadway and water-rich coal seam was separa-ted,the shaft water inflow was minimized,the grouting and blocking water task was finished beyond expectation-the auxiliary shaft lining total water inflow decreased from the original 150 m3 / h (maximum 200 m3 / h) to 11 m3 / h when completed,the grouting and blocking water rate reaching to 93% . Moreover,the results show that sealing the large amount of effluent from water-rich coal seam was realized with a good engineering effect,proving the remarkable a-chievements of water prevention and control security technology.