Quantification of river flood risks is a prerequisite for floodplain management and development. The lower Yellow River (LYR) is characterized by a complex channel–floodplain system, which is prone to flooding but inhabits a large population on the floodplains. Many floodplain management modes have been presented, but implementation effects of these management modes have not been evaluated correctly. An integrated model was first proposed to evaluate the flood risks to people’s life and property, covering an improved module of two-dimensional (2D) morphodynamic processes and a module of flood risk evaluation for people, buildings and crops on the floodplains. Two simulation cases were then conducted to validate the model accuracy, including the hyperconcentrated flood event and dike-breach induced flood event occurring in the LYR. Finally, the integrated model was applied to key floodplains in the LYR, and the effects of different floodplain management modes were quantified on the risks to people’s life and property under an extreme flood event. Results indicate that: ① Satisfactory accuracy was achieved in the simulation of these two flood events. The maximum sediment concentration was just underestimated by 9%, and the simulated inundation depth agreed well with the field record; ② severe inundation was predicted to occur in most domains under the current topography (Scheme I), which would be alleviated after implementing different floodplain management modes, with the area in slight inundation degree accounting for a large proportion under the mode of “construction of protection embankment” (Scheme II) and the area in medium inundation degree occupying a high ratio under the mode of “floodplain partition harnessing” (Scheme III); and ③ compared with Scheme I, the high-risk area for people’s life and property would reduce by 21%–49% under Scheme II, and by 35%–93% under Scheme III.