Lake Poyang is one of the two river-connected lakes in the Yangtze River system, which plays a critical role in regulating the water level of Yangtze River, containing water, improving the local climate and maintaining the ecological balance of the surrounding areas. The construction of Lake Poyang Hydraulic Project might lead to changes in the hydrological situation and hydrodynamics of the lake. This study developed a two-dimensional hydrodynamic model of Lake Poyang based on MIKE 21, and selected 1954 and 1998 mega-flood years and 1991 Yangtze River backflow year as the typical years of operation period and 1995 as the typical year of construction period. The developed model was used to predict the changes of water level and flow of Lake Poyang before and after the construction of the hydraulic project according to the construction and operation scheduling scheme of the planned Lake Poyang Hydraulic Project. The impacts of the project on the flood dynamics in the main stream of Yangtze River, the lake area and its inlets were quantitatively investigated. Our investigated showed that the impact of the hydraulic project on the flood dynamics of Yangtze River main stream, the lake area and its inlets would be similar in different typical years. The impacts on flood control of Yangtze River, the lake area and its inlets would be relatively small during flooding period, backflow period and construction period I. The congestion of lake level in construction period Ⅱ would be up to 0.237 m, implying certain impact on flood control of the lake area and its inlets. The impact of the project on the water level of Xingzi, Duchang, Kangshan and other hydrological stations would be similar. The closer to the inlets of Lake Poyang, the smaller of its impact on water level. Overall, Lake Poyang Hydraulic Project would lead to high water level congestion in Lake Poyang in flood year, lower water level in the lake in backflow year and lower flow velocity in the lake, but with limited changes of above-mentioned variables. Therefore, the construction and operation periods of the project would have limited impact on flooding during the flooding period.