Abstract: A method confirming the flood submerged area is provided.The method adopts the digital elevation model (DEM),GIS,hydrodynamic model and object-oriented data base (OODB) to determine the submerged area.The steps are as followings: first,the whole research region is divided into some small subcatchments and the DEM of the region is established; then the submerged area is distinguished from the whole region under the condition of the given water level calculated by the hydrodynamic model,and is calculated and visualized based on the flood water level,GIS and the DEM data set; last,the submerged area map is overlaid with raster data converted from other thematic vector maps as a result map.Further more,the quantitative evaluation of flood damage can be easily achieved with object-oriented database of social and economic data.The precision of this method mainly depends on the spatial resolution of the DEM.The method was applied to Fenghua River watershed of Zhejiang province,and got a satisfactory result.