Abstract: According to the mining of C₉ coal seam in Daping coal mine, Yunnan province, the coal seam is faced with the problems of poor permeability, high gas content, long time of pre drainage reaching the standard, and maladjustment of production continuity, etc.Theoretical analysis and experimental investigation are used to analyze the mechanism of increasing permeability and reasonable technical parameters respectively, find the reasonable cutting pressure of C₉ coal seam is 75 MPa, the reasonable chip removal amount of single seam is 0.36 t, the radius of slot is about 1.66 m, the reasonable cutting time of single seam is 7 min, and the reasonable spacing between slots is 5 m.The test results show that after adopting ultra-high pressure hydraulic slotting in C₉ coal seam, the concentration and pure flow of gas extracted by drilling are increased by about 2.14 times and 2.74 times, and the time of reaching the standard is shortened by about 63.7%, which effectively guarantees the safety and efficiency of the mine production.