DEM data and GIS spatial analysis technology were used to construct a flood and inundation analysis module. Polder areas were generalized into a zero-dimensional storage unit to realize elaborate simulation of polder areas. Coupled with the refined hydrological and hydrodynamic model of the Taihu Basin, a reliable flood inundation simulation model was established. The flood event occurred in 2016 was selected for model verification. Comparison of water levels and real flood inundation distribution between the simulation and observation from the Taihu station and other representative stations shows that the constructed model is reliable. The verified model was used to simulate the flood inundation of the Taihu Basin under the scenario of plum rain encountering typhoon rainstorm. The simulation results are scientific and reasonable, which can provide technical support for basin flood risk management.