In this paper, according to the pattern developed by the predecessors, the operation of the two kinds of grids is calculated and the extrapolation is applied to after the calculation of the two kinds of meshes. The extrapolation is based on the error derived from the numerical discretization method, and it is intended that the results after extrapolation be better than the results of the two coarse grid calculations. This paper first uses the three different equations to carry out the error derivation and extrapolation application, illustrating the practical effect of the method. About the relevant sections of the debris flow, the calculation of the error of the model itself is derived. Then by different groups of experiments, Observe the degree of agreement between the theory and the actual results, to verify the results of the use of extrapolation.