Abstract: In order to determine the effective influence radius of gas drainage through borehole quickly and accurately, the exponential relationship between draina ge quantity of boreholes and drainage time was established based on the mathematical model of one- dimensional radial flow of gas. On the basis of the law of mass Co nservation and Darcy law, calculation formula of drainage radius was derived and mathematical relationship between drainage radius and coal seam parameters and dr ainage time was established. By using this method, drainage radius of Xinfeng Coal Mine No. 25021 Coal Mining Face was calculated. The calculation result was 2.70 ~ 3. 72 m within 60 days and was similar to the site measurement. Meanwhile, the functional relationship between drainage radius and drainage time was researched. T he results showed that with the increase of drainage time, the drainage radius increased gradually. When the drainage time reached to 60 days, the drainage radius rea ched to 96.46% ~ 98. 54% of limit value. After that, the drainage radius increased very slowly.