Abstract: In order to improve the gas extraction effect of the pre-pumping borehole along the bedding, taking the 1202 working face of No.12 coal seam of Hongyang No.2 mine as the engineering background, the research on the reasonable sealing depth is carried out.By analyzing the factors such as roadway excavation, it is divided into pressure relief zone, plastic zone and elastic zone according to the influence range.By means of theoretical analysis and numerical simulation, the reasonable sealing depth is determined to be 15 m.Based on this conclusion, 40 gas pre-pumping boreholes with sealing lengths of 8 m, 12 m, 15 m, 18 m and 20 m are arranged in the return air downdraft trough of 1202 working face.Five groups of field tests were carried out under different sealing depths.The results show that with the increase of sealing depth, gas extraction concentration and pure quantity also rise.However, when the sealing length exceeds 15 m, the improvement effect is not significant.Therefore, considering technical and economic factors comprehensively, the reasonable sealing length of bedding drilling in this working face should be 15 m.