Abstract: The numerical calculation method is one of the common means to solve problem of radon migration mechanism. In this paper, by taking a semi-infinite homogeneous porous radioactive medium as calculation model, we deduced propagation equation of radon migration, and calculate the surface radon migration and precipitation behavior of radioactive medium only by diffusion or convection. The results show that the radon concentration distribution law in semi-infinite large homogeneous porous medium obeys exponential distribution. In the process of radon migration based on diffusive convection, the radon exhalation rate of the radioactive medium depends on the concentration of radon in the radioactive medium pore and the convection velocity of the fluid. The radon exhalation rate is determined by the pore concentration under the effect of diffusion; and the rate of radon precipitation is determined by the direction of fluid flow and the velocity of flow under the action of convection. The results will be applied to the measurement of shallow buried thin bedrock coal seam surface radon detection results, and the calculation results agree with high degree of research results.