Abstract: For increasing the coal seam permeability, improving the gas extraction rate and reducing the risk of coal and gas outburst, the hydraulic fracturing permeability improvement technology is proposed in underground mine of Xing'an Coal Mine. Based on the field test of hydraulic fracturing, in order to identify the proper water pressure, the numerical simulation is used to calculate the critical water pressure of initial crack, and the simulation result of water pressure is 12.4 MPa. The test of numerical simulation and field experiment show that underground hydraulic fracturing can improve the efficiency of gas drainage.