On the basis of previous researches, an equation for radon movement in Quaternary overburden over the fault has been established on the assumption that the overburden is stable. The boundary conditions are given in this paper. The numerical simulation of radon distribution in the overburden and the influencing factors are discussed. It is shown that there exists an obvious anomaly in the overburden over a fault, and its distribution is affected by the thickness of the overburden, the width of the fault, the diffusion coefficient of radon, and the convection velocity of radon.