Taking the flood detention area around Hongze Lake at the junction of the middle and lower reaches of the Huaihe River Basin as the research object, the one-dimensional and two-dimensional hydrodynamic models are coupled based on the tight coupling technology. Based on the loose coupling technology, climate model is coupled with hydrological model and hydrodynamic model. The climate-hydrologic-hydrodynamic one-way coupling of the complex system of the basin, river network, flood storage and detention area and lake is realized, and the water flow evolution in the complex river network area under the influence of climate change is simulated. The results show that the constructed climate-hydrologic-hydrodynamic coupling model has good simulation ability and adaptability for flood routing in the flood detention area around Hongze Lake. Climate change will increase the magnitude of future floods in the Huaihe River Basin, and increase the flood risk in the flood detention area around Hongze Lake.