According to the determination of basic parameters of gas in coal bed, bedding in the laboratory on drilling under the condition of reducing gas concentration, flow and drainage radius parameter change rule has carried on the numerical simulation, and the way of the valve in Bai shan ping coal mine 1265 coal mining face verifies the effect of the drainage radius. It is found that the numerical simulation results are in good agreement with the measured results. The final result shows that the mining face in order to ensure the safety in production, the hole diameter should be better with 75-100 mm.