Abstract: The determination of the reasonable sealing depth of gas drainage boreholes in coal seam is a key technology for ensuring the tight sealing of boreholes and improving the gas drainage effect. In order to determine the reasonable sealing depth of the holes drilled along C₂ seam in Bailongshan Coal Mine, study and field test were carried out on the reasonable sealing depth of the boreholes along the seam based on the stress zoning characteristics by taking the drilling cuttings gas desorption index K₁ and the drilling cuttings weight S in the coal roadway heading face as the basic data. The results showed that 0 to 3 m range of the coal roadway sides in C₂ seam was the pressure relief zone, 3 to 7 m range was the stress concentrated zone and the range beyoud 7 m was the original stress zone; the reasonable sealing depth of the holes drilled along C₂ seam should be 7 m or more; the gas drainage concentration of the test hole was 9% to 45%, an average of 27%, the gas drainage concentration increased by 1.8 to 5.6 times; the negative pressure of the borehole gas drainage was 14 to 16 kPa, increased by 1.7 to 2.0 times, so the effect was obvious.