Abstract: For the safe production of coal mine,many coal mines have established various gas drainage systems.For the design of the optimum gas drainage scheme and the accurate forecast of the gas state in the target,a numerical simulation for gas drainage is necessary.But one of the main problems is that in the design of gas drainage schemes there is no scientific basis,so the study for the incidence of underground roadway to gas content in the coal seam is performed in the view of the numerical simulation in this paper.Via the simulation software Comet II,for two reservoir models with different permeability,a simulation study has been completed.By the analysis for the incidence of underground roadway,after it exists for 180,360,and 730 days,some view has been obtained.