Abstract: In order to improve the sealing effect of extraction drillings, a device was developed to detect the leak location of the drilling and plug the hole with secondary grouting. The application test was carried out for the coal seam pre-drilling in Yuwu Coal Mine. On the basis of detecting the leak location of drilling, the reasonable grouting depth in drilling was defined. Then the drilling was plugged with secondary grouting, and the variation of gas concentration (methane volume fraction) in the plugging drilling of secondary grouting was analyzed. The results show that the gas leak location in the extraction drilling has a great influence on the gas concentration, the gas concentration shows a decreasing trend from the bottom of the drilling to the orifice, and the smaller the gas concentration is, the more serious the gas leakage is; the air leakage is the most serious at the location 16 m to 17 m away from the orifice, while the air leakage is relatively reduced at the location 18 m to 19 m away from the orifice. Considering comprehensively, the depth of secondary grouting in the drilling is set as 16 m to 19 m; the drilling with gas concentration above 30% in the second grouting to plug the gas leakage account for 58.8%, and those with extraction concentration reaching 15% to 30% account for 23.5%, indicating that the technology of the second grouting to plug the gas leakage can effectively improve the gas extraction concentration of the drilling.