Abstract: Aiming at the problems of low efficiency and high cost of hydrogen sulfide treatment in working face caused by the full contact between alkaline absorption liquid and hydrogen sulfide in coal seam through multi-borehole method in common pre-injection process, this paper adopts high-pressure pre-injection hydrogen sulfide absorption liquid to absorb hydrogen sulfide in coal seam, and injects hydrogen sulfide absorption liquid into coal seam through high-pressure water injection drilling.Through theoretical analysis and Gaojiapu field test, the optimal sealing length of thick coal seam in Gaojiapu Coal Mine is studied.The results show that the increase of sealing length will directly affect the maximum water injection pressure that the sealing material can bear.When the sealing length is less than 9 m, the maximum water injection pressure that the sealing material can bear is proportional to the sealing length.When the sealing length is greater than 9 m, the increase of sealing length has no obvious effect on improving the maximum water pressure of sealing material.After using the capsule expansion hole sealing device, the sealing efficiency is improved by more than 70%.