Abstract: In order to study the gas drainage effect after hydraulic fracturing, PFC^2D numerical simulation is combined with COMSOL numerical simulation, and a geometric model image pixel level processing method is proposed. This method imports the PFC^2D fracture geometric model after hydraulic fracturing into COMSOL software, completes the combination of two numerical simulation software, and realizes the numerical simulation of gas drainage in hydraulic fracturing coal seams. The research results show that compared with the water injection pressure of 20 MPa, the range of water injection fracturing is larger, the number of fractures is larger, the fracture expansion range is larger, and the fracturing effect is good; and under the same extraction time, the gas extraction range and drainage flow of 40 MPa water injection fracturing are large. Hydraulic fracturing can improve the gas extraction effect of coal seams, which is consistent with the actual engineering application effect.