Abstract: In this paper, a 1 D and 2 D combined numerial model of flood propagation is presented. In the model, the partial cell parameter is applied to treat complex boundaries in the flood plain, such as roads, embankments, blocks and culverts. Using this model, the propagation of the diverted flood in the detention basin is simulated successfully. In order to map the risk, a fuzzy model is used to divide the whole basin into 5 sub areas. Then, based on the flood risk map, a quantitative risk analysis system is developed to predict, control and scale the risk of the flood.