Abstract: In the work of coal mine gas drainage, getting effective drilling drainage radius could reasonably layout the drainage drilling, and get the optimal design, least engineering quantity, best drainage effect. The paper analyzes the relationship between the ability of gas drainage and the influence factors such as gas pressure, drilling gas attenuation coefficient. The paper predicts the range of drainage influence radius through the mathematic model, proposes the design scheme for determining the No.2 coal seam gas drainage influence radius in Julong Coal Mine.