Abstract: According to the characteristics of high gas content, poor permeability of coal seam and fast attenuation rate in Ⅱ₁ coal seam of Jiulishan Mine, we implemented drilling hydraulic fracturing and permeability improvement measures. In order to investigate the influence law of gas occurrence in the affected area of hydraulic fracturing, the relevant investigation is carried out in and out of the affected area of fracturing. The results showed that the permeability of coal seam increased and the effect of extraction was greatly increased in the range of fracturing, and the pure flow rate of single drilling was increased by 1.65 to 2.36 times. After fracturing, the coal stress is moved from the fracturing zone to the outside, and the stress concentration zone is formed on the edge of the influence range of fracturing, the pressure of the ground and gas increases, the gas pressure gradient increases, and the initial borehole flow increases.