Abstract: Abstract: The phenomenon of H2S over limit occurrs during the development of 13# coal seam in Shaping Coal Mine. In order to prevent the harm of H2S to workers and affect the safety production, the method of injecting alkali into coal seam is used to treat H2S. The alkali solution with sodium carbonate as the main component is chosen by comparing the absorption effect of different alkali solution. The H2S concentration in the coal water is 150ppm, the H2S concentration in the coal is 130ppm, and the H2S concentration in the air is 30ppm, which belongs to the high H2S coal mine. COMSOL multiphysics software is used to carry out numerical simulation on the process and effect of coal seam alkali treatment of H2S.The simulation results show that: Alkali infusion pressure and alkali liquor diffusion effect are positively correlated, and the longer the alkali infusion time, the greater the diffusion range of the alkali liquor. To achieve better results, we recommend selecting an alkali infusion pressure of 4MPa and an alkali infusion time of 48h, and using porous alkali infusion with a pore distance of 8m. A 30-day alkali injection test is carried out in 13# coal seam. After alkali injection, the concentration of H2S in roadway air decreases from 32ppm to about 3ppm, and the concentration of hydrogen sulfide stabilizes at about 3ppm during mining, indicating that coal seam alkali injection can effectively control H2S over limit.