Abstract: Facing to the field of flood simulation,a new "Ring" method for flood has been introduced in the paper,which is based on the DEM data and flood's classical principle. Aim at the small region,the new method tries to combe the DEM data's characters and GIS' advantages to implement flood's simulation and forecasting. In succession,according to the new method,a 3D flood simulation and forecasting system have been design and implemented,which is used to supply exact and available information to make flood map,flood prevention and other interrelated works.