Abstract: Aiming at the problems of the coal seam of Zhaogu No.2 Coal Mine, such as the hard coal seam, low permeability, poor drilling gas drainage effect and large amount of drilling engineering, it is proposed to use ultra-high pressure hydraulic slotting technology to improve gas drainage efficiency. Based on the principle of stress wave, the mechanism of high-pressure water jet coal breaking is analyzed, and conical convergent nozzles which can effectively improve the jet impact force for hard seam conditions and fixed-point impact slitting methods for hard seam conditions are developed. Field tests show that, for hard coal seam conditions, the average single-edged coal output of the slotted hole is about 0.18t, and the equivalent slotted radius is 0.99 to 1.57m. The natural gas emission amount after slotted is 11.3 times that of ordinary drilling. The scalar quantity is 3.8 times higher than that of ordinary drilling, and the effective radius of drilling extraction is increased by about 90% compared to ordinary drilling. Ultra-high pressure hydraulic slotting technology can effectively solve the gas drainage problem of low-permeability hard coal seams.