To assess the dynamic risks of flood detention basin operations and support precision-based utilization, this study developed a flood risk assessment system for detention basins by integrating remote sensing and GIS technologies. By employing a two-dimensional hydrodynamic model and a set of operation schemes based on flood diversion volumes, the system simulates flood propagation at various stages during the diversion process in detention basins, clarifying the dynamic risk characteristics of their operation. A risk analysis was conducted on the Honghu Dong Flood Detention Area as a case study, yielding the following results: (1) For every 100 million m³ increase in diverted flood volume, the average water level in the Honghu Dong Flood Detention Area rises by 0.57 m. (2) Under the combined effects of loss rates and land cover distribution, direct economic losses increase most rapidly within the diversion volume range of 2-4.5 billion m³. Indirect economic losses and population displacement grow fastest during the initial diversion stage (diversion volume below 0.5 billion m³). (3) When the Honghu Dong Flood Detention Area diverts 2 billion m³ of floodwater, the entire basin is inundated, requiring the full evacuation of 183,700 people within the area. When diversion exceeds 2.5 billion m³, economic losses shift from being predominantly indirect to primarily direct, with secondary and tertiary industry losses stabilizing at 980 million RMB. At diversion volumes above 3 billion m³, the fishery output within the basin is completely lost, amounting to approximately 3.6 billion RMB in losses. When the Honghu Dong Flood Detention Area diverts 6 billion m³, direct economic losses reach about 17.36 billion RMB, and indirect economic losses total approximately 6.55 billion RMB. These research findings provide technical support for the scientific operation and risk management of flood detention basins.