Abstract: In view of low permeability characteristics of No.3 coal seam in Changping Coal Mine, the effective radius of gas drainage of bedding drill hole was measured and analyzed by improving sealing process with polyurethane-expansive cement and use of hole pressure method, and determined effective radius of gas drainage of bedding drill hole of No.3 coal seam of Changping Coal Mine is 2.5 meters. It avoids the phenomenon of empty gas drainage area, string holes and hole collapse in gas drainage process, and provides an important basis for reasonable arrangement of gas drainage drill hole.