Abstract: The seepage of groundwater in rock joints may result in water-inrush from surrounding rock or failure of support during excavation.To study the seepage behaviors of Beishan granite fractures, radiation flow seepage tests on specimens with a single fracture were conducted using the MTS815 rock mechanics test system.The variations of flow quantity of the fractures under different normal stresses are obtained.The influence of geometric characteristics of fractures on seepage behaviors is analyzed.Subsequently, the 3D distribution characteristics of the fracture voids are quantitatively characterized by the variogram.The equivalent hydraulic aperture calculation model of radial flow(CA model), which considers the influence of the 3D distribution characteristics of the fractures and contact ratio, is established.The 3D distribution of fracture voids can be characterized by 3D distribution coefficient(CA).The larger the CA value is, the more uneven the distribution of fracture voids is.Meanwhile, the CA model can be used to quantitatively describe the functional relationships between the equivalent hydraulic aperture of fracture and the mechanics aperture, the convex contact ratio and the 3D distribution coefficient of the fracture.In addition, a comparison shows that the model calculation results are in good agreement with experimental data, indicating that the established CA model is reasonable and effective.