Abstract: In order to accurately investigate the effective extraction radius of this coal seam borehole, the relationship between the gas flow rate of the borehole and the time was established based on the theory of gas flow in the coal seam. the index standard of experimental investigation under different gas occurrence conditions was analyzed. the extraction standard time t was determined by using the gas content and extraction rate index method in combination with the actual situation of Fei tian coal mine in order to highlight the coal seam mining. finally, the correlation between the extraction radius r and the extraction time t was obtained as r = 0.7005 ln t - 2.0749. The investigation results show that the effective extraction radius increases with time and gradually approaches the limit effective extraction radius of 2m. When the extraction time is 37d, 89d, 168d, 318d, the corresponding effective extraction radius is 0.5m, 1m, 1.5m, 2m. The field test proves that the drilling flow method can be used to investigate the extraction radius of drilling holes in this coal seam.