In response to the changes in the frequency and intensity of flood disasters caused by extreme precipitation, which in turn lead to an increase in the probability and risk of the activation of flood storage-detention areas (FSDAs), a one- and two-dimensional coupled hydrodynamic model for Dongdian FSDA was developed. The model was calibrated using remote sensing and hydrological station monitoring data as well as field-based flood mark surveys. A comprehensive retrospective analysis was conducted of the flood propagation process and inundation characteristics in Dongdian FSDA during the “23·7” catastrophic flood in the Haihe River Basin. The results show that the simulated inundation range is in good agreement with the remote sensing monitoring results. The maximum water level errors at each hydrological and water level station were less than 20 cm, the peak discharge deviations remained below 5%, and the peak arrival time discrepancies were within 2 h. The error of the inundation depth of the flood mark was less than 30 cm, and 86% of the points had an error of less than 20 cm, demonstrating good effect of simulation. The Xingaifang flood peak traversed the flood diversion channel and Dongdian FSDA in 11 h and 7.3 d, respectively, and the peak attenuation was 12% and 40%, respectively. The flood propagation in the FSDA was slow, with a large inundation depth and a long inundation duration. About 65% of the area had a flow velocity of less than 0.2 m/s, an inundation depth of greater than 2 m, and an inundation duration exceeding 30 d, which included 38% of villages, 67% of farmland, and 96% of the greenhouse structures.