Abstract: To reduce the gas harmful of No.2 coal seam in Chiyun coal mine, discharge local gas efficiently, the method of drilling gas flow is used to determinate advance borehole effective influence radius of No.2 coal seam, and the method of outburst index is used to define the result of determination finally. The result shows that the way of using the methods of drilling gas flow and outburst index comprehensively to determinate advance borehole effective influence radius will make the data more pertinence for design and operability for construction, and will apply practicability direct to the No.2 coal seam gas treatment in Chiyun coal mine.