In order to improve the extraction effect of gas extraction holes in Shangshe Mine, "two plugging and one injection" slurry sealing process with pressure was introduced, and the test of sealing and thickening of gas extraction holes in this coal seam was carried out in 15308 air return roadway. The test results showed that the average extraction concentration and pure extraction volume of single hole of this coal seam borehole after two plugging and one injection with pressure slurry sealing technology were nearly 1.5 times higher than that of polyurethane sealing, which ensured the durability of gas extraction system and met the needs of safe and efficient production of the mine.