Abstract: The simulation of flood routing and the computation of flooded areas are key tasks for flood control, damage estimation and emergency management. Meanwhile, it is necessary and possible to apply numerical simulation, database and GIS technologies in the research field of floodcontrol management as well as to the computation and analysis of flooded area simulation by GIS. This paper, taking the lower reaches of Haizi reservoir basin as an example, discusses the application of approaches and methods of GIS in the computation of flooded area and in the establishment of flooding analysis system for flood prevention and mitigation. At first, software and hardware environment, system structure, contents, main functions and technical characteristics of application system are expounded. Then, on the basis of obtained data, present work and current resources, a GISbased flooding analysis system was established by adopting numerical simulation, digital elevation model. The system realized such major functions as map manipulation, information query, information management of hydraulic structure behavior, computation and analysis of flooded areas, management of flood control, information issuance and statistical output, which was characterized with composite structure of Client/Server mode and Browser/Server mode, massive data management, metadata organization and modular development. In addition, the system was applied for the flood control and mitigation management of the reservoir valley for Beijing bureau of water resources. At last, it is concluded that the adopted technical methods and numerical model can simulate flood routing, compute flooded areas and assess flooded losses, thus providing a scientific basis for the fast assessment of flooded losses and decisionsupport service of flood control, and that the computation precision of flooded areas and the veracity of disaster loss assessment and forecast are mainly dependent on the quality of spatial data and the complete extent of relative statistical data.

Key words: geography information system, flooded area, computation and analysis, floodcontrol management