In order to accurately determine the reasonable spacing of gas extraction boreholes and improve the extraction efficiency, this study established a coal seam gas extraction model based on the gas flow theory, and used COMSOL Multiphysics numerical simulation system to analyze the influence of extraction time, borehole diameter, coal seam permeability, extraction negative pressure and initial gas pressure on the effective extraction radius. The results show that the effective extraction radius increases significantly with the increase of extraction time and coal seam permeability. The influence of negative pressure and borehole diameter on it is relatively small. The effective extraction radius increases first and then decreases with the increase of initial gas pressure. The field measured data of No.5 coal seam in Qianjiaying Mine are compared with the simulation results, and the two are in good agreement, which verifies the reliability of the model. This study has important engineering guiding value for optimizing the design of on-site gas extraction boreholes.