Drawing flood risk map is an important way in flood mitigation project. It not only can effectively reduce losses caused by flooding, but also provide flood forecasting in time. In this paper, use the inversion technology of GIS , establish the flood model for flood risk analysis, for flood storage and detention areas partition dangerous degree, and calculate the flood region risk map in different application. The flood risk map can provide basis for decision making by flood-control headquarters at all levels, and also can provide a scientific basis to create a long-term management mechanism for the flood storage and detention areas.