As an important means of increasing coal seam gas production, hydraulic fracturing technology has been widely used in coal mine gas control in recent years. However, the mechanism of hydraulic fracturing gas extraction and production still needs to be further explored. In this paper, the 3#^{coal seams in Yangquan mining area}is taken as the research object. Through the combination of isothermal adsorption experiment, quantum chemical analysis and numerical simulation, it is revealed that the mechanism of hydraulic fracturing gas production is mainly manifested in two aspects: H2O replacement CH4 and hydraulic fracturing. The specific results are as follows: ①The influence radius of long borehole hydraulic fracturing technology in 3^# coal seam of Yangquan mining area is 35~58 m. Compared with the ordinary long borehole without hydraulic fracturing, the gas extraction concentration is increased by 19.46~70.05 times, and the 100 m borehole extraction purity is increased by 22.22~110.00 times. ②When n(CH4)/n(H2O)<4, the adsorption stability of CH4 on the surface of coal molecules decreases with the increase of n(H2O). When n(CH4)/n(H2O)≥4, under the dual action of hydrogen bond and van der Waals force, the increase of H2O cannot attract CH4 to move, indicating that hydraulic fracturing technology can promote gas desorption in coal, but too much liquid injection is not conducive to gas desorption. ③The vertical stress of 3^# coal seam in Xinjing Coal Mine is greater than the maximum horizontal principal stress. Hydraulic fracturing forms a vertical main fracture, and its end develops a complex micro-fracture system with fan-shaped and ge-shaped distribution, which effectively expands the communication range of coal and rock mass and provides a key channel for gas seepage. This study clarifies the micro-mechanism and macro-effect of hydraulic fracturing to promote gas desorption and seepage from the two dimensions of molecular competitive adsorption and macro-crack propagation and provides a theoretical basis for hydraulic fracturing gas production in coal mines.