As the main reason for soil water erosion, the overland flow process should be simulated precisely to understand the mechanism of slop soil erosion process. Developed based on the kinetic theory, Lattice Boltzmann method has advantages of concise programming, parallel computing and complex geometric adaptability, etc. So its application in field of fluid motion becomes more and more extensively. The detailed steps about applying Lattice Boltzmann method to the movement of overland flow was given firstly, and then its validity was verified through artificial simulated rainfall experiment. The results indicate that if the time is processed by multi-scale approach and the space is not, the equilibrium distribution function is determined by the method of undetermined coefficients and multi-scale analysis, the distribution function about nodes of the upper boundary is replaced by the equilibrium distribution function through regarding the macroscopic upper boundary conditions as limiting conditions, and the distribution function about nodes of the lower boundary is set by extrapolation format of distribution function, Lattice Boltzmann method will successfully become a motion equation solver. The errors of runoff depth are within ±11%.