Abstract: To determine the effective drainage radius of drilling is the key of coal mine gas extraction.This paper simulates the process of fluid flow in porous media by using the FLUENT software,in which the porous model is used to add some resistance properties which can characterize the properties of the porous media.The result shows that:1the theoretical drainage radius of this working face is 1.9 m,and the gas drainage spacing should be designed at 4 m;2the change of coal seam permeability can influence gas migration resistance,which can affect the gas migration velocity greatly;and the suction pressure can influence the gas migration motivation,which can affect the borehole gas flux to a certain extent;3 The simulation results and test results were unified well.