Accurate data of the ground elevations is required in the analysis of inundation flows. In order to represent accurate topography, we have to use fine grid. But the fine numerical grid increases in the number of the grids. So, high-speed calculation is difficult. In this paper, we developed the new approximation method of ground elevation, which is called "Adaptive grid for the topography". The method has flexible expression to approximate to the ground elevations, and decrease the number of the grids.<BR>Next, we developed the application system for the calculation results. The system is used by geographic information system, provides the many functions. The functions are viewer of the calculation results, summing up the square of the flooded area and flooded house, and finding the route of refuge.