Borehole extraction of coal seam gas is one of the commonly used extraction measures in mines, which plays a vital role in mining activities. In order to solve the problems of non-uniform diameter of drainage boreholes and unreasonable spacing of boreholes in underground coal mines, and to avoid the invalid overlap of blank areas or boreholes in the process of designing the layout of drainage boreholes, this paper uses the extraction volume method to study the effective extraction radius of bedding boreholes. Based on the field data, the influence of two common apertures ( Φ94 mm, Φ108 mm ) on the effective extraction radius was studied by theoretical analysis and mathematical calculation. The results show that the variation of gas extraction purity and extraction time conforms to the exponential equation, and the effective extraction radius increases with the increase of borehole diameter. When the diameter of the borehole is the same, the larger the spacing between the boreholes, the longer the pre-drainage time to achieve the gas extraction standard ; when the arrangement spacing between boreholes is the same, the larger the diameter of the borehole, the shorter the pre-drainage time to achieve the gas extraction standard, which can provide an important reference for the extraction design, construction period calculation and economy.