According to the topography, geomorphology, middle and small rivers, drainage system of Xiqing District in Tianjin, a rainstorm and flood disaster simulation model of small and mediumsized rivers in Xiqing District of Tianjin is established. The objects of the simulating model are the geomorphology and flow movement of open channels. Using the boundary condition of the model based on the dynamic water levels in 14 secondary rivers, an operational experiment for the risk assessment of flood and waterlog disasters in Xiqing District is carried out. The rainstorm and flood disaster simulation model is used in the experimental research for the rainstorm and flood disaster caused by the rainstorm on 20 July 2016. Four simulation schemes are designed to evaluate the waterlog process caused by the high water level and rainstorm. These simulation results are directly used in contrasting and assessing the actual disaster caused by the rainstorm on 20 July 2016.The experiment results indicate that the model can objectively reflect the waterlog disaster caused by the rainstorm and the river water level variation.