The invention discloses a medium-hard coal seam bedding drill hole gas treatment method. The method comprises the following steps: measuring an average f value of a coal seam by coring, determining hydraulic slotting process parameters, determining an extraction radius r1 after hydraulic slotting in the coal seam, determining an extraction radius r2 after hydraulic slotting and liquid CO2 phase change fracturing, rearranging drill holes according to the numerical value of r2, performing hydraulic slotting and liquid CO2 phase change fracturing, sealing the holes, conducting connection with anunderground extraction system, and performing extraction effect inspection. According to the method, firstly, a seam along the direction of a coal seam is directionally cut by utilizing a hydraulic slotting technology, pressure relief disturbance is conducted on the coal seam, then high-pressure gas generated after liquid CO2 phase change is used for directional cracking along the seam, and therefore the cracking effect can be effectively improved, coal seam gas extraction is accelerated, the gas treatment time is shortened, and safe production of a working face is guaranteed.