Abstract: In order to improve water level forecasting accuracy in plain tidal river network area, and tackle the problem of low efficiency in real-time flood risk assessment and "Four-Pres"(forecast, early-warning, preview and response plan)difficulties in Taihu Lake Basin, a coupled atmospheric-hydrological modelling system of Taihu Lake Basin that is composed of the hydrology and hydrodynamic models and the rapid assessment model for flood inundation risk region based on hydrological method was established, which were driven by ECMWF grid and sub-region precipitation forecast during the typhoon In-Fa period in 2021.The risk region of water exceeding the alarming and guaranteed level for the representative stations over the Taihu Lake Basin was predicted by the hydrology and hydrodynamic model that is based on river network polygon, distributed dynamic unit hydrograph of flow conflux model.The flood inundation risk of the Taihu Lake Basin was predicted by the rapid assessment model for flood inundation risk region based on hydrological method.The results demonstrated that the coupling of precipitation forecast grid, partition and river network polygon were realized in the coupled atmospheric-hydrological modelling system.The problem of precipitation and runoff spatial homogenization was tackled by the hydrology and hydrodynamic model.Compared with the results given by partitioned precipitation forecast, the risk region of water exceeding the alarming and guaranteed level, flood inundation risk area given by grid precipitation forecast were consistent with observation.The coupled atmospheric-hydrological modeling system during the typhoon In-Fa period provided decision support for the scientific flood peak staggered regulation of the basin flood and sub-region waterlogging, which mitigated flood defense pressure of the downstream region and acquired remarkable social and economic benefits.