In response to the lack of joint regulation methodsof the complex engineering system of surface-underground reservoirs in coastal small and medium-sized river basins, which leading to difficulties in flood resources utilization, the structure and function of surface-groundwater reservoir system was analyzed, the surface reservoir regulation and dynamic processes of rivers and groundwater under gate dam regulation were quantitatively simulated, and the intelligent replacement models to improve the calculation speed of hydrodynamic processes were used.A multi-time scale model coupling nesting method of hour/day/month was developed to construct a joint regulation model of surface-underground reservoirs that takes into account calculation accuracy and optimization efficiency. This model realized the unified allocation of floods, surface groundwater interactions, and water supply, which can provide new ideas and technical support for the utilization of floodwater resources in coastal small and medium-sized river basins. Keywords:flood resources utilization;surface-underground reservoir system; joint regulation; multi-time scale nesting model; coastal small and medium-sized river basin