In order to study the meso-hydraulic characteristics of radiation flow in a parallel single fracture, a k-ε calculation model based on turbulence RANS is established. The simulation results show that the radiation flow in the parallel single fracture presents the characteristics of “atypical radiation flow”, and a preferential hydraulic channel is usually formed; because the evolution of the vortices narrows the flow channel, the closer to the preferential hydraulic channel or the radiation center, the stronger the flow velocity and vortex intensity become; the rise of water pressure at the radiation center leads to the increase of fracture flow, and the earlier the preferential hydraulic channel is formed and more stable it is, the wider the fracture become and the more significant the turbulence effect of the fracture is, but the fracture flow is dominated by radial turbulence; the fracture contact surface redistributes the preferential hydraulic channel, which decreases the seepage ability of the fracture, and the contact rate is negatively correlated with the fracture flow; the wall slip can be either obstructive or beneficial to the fracture flow, depending on the direction and velocity of the slip. It is found that the inlet water pressure, fracture width, contact rate and wall slip have a significant effect on the radiation flow, and these findings can provide a reference for the study of radiation flow in complex fractures.