Abstract: A discrete model for random media is employed to simulate the distribution of railway ballast. The calculation simulation model for railway ballast is built by random filling in the meshes of FDTD method, and the intensities of the transient electromagnetic scattering field are calculated. Then the incoherent scattering field is calculated and analyzed to obtain the electromagnetic parameters for the distribution of the railway ballast. The numerical analysis result shows that there exists an exponential function relationship in a certain range between the obtained parameters and the porosity of railway ballast. Therefore, it can be concluded that applying the electromagnetic technology to detect the porosity of railway ballast is possible.