Abstract: There are some problems in the current mathematical model of the optimal operation of reservoir floods, such as continuous adjustments of the discharge gate and sudden change in discharge between time periods. In response to these problems, the model of the optimal operation of reservoir flood control is divided into the instantaneous outflow model and the constant outflow model. In a basic flood control system consisting of a reservoir and a flood control station, with a constant outflow rate considered the decision variable, a compensative reservoir flood control regulation is developed through the confluence curve of the Yangtze Water Resources Commission; this system can meet the requirements of refinement and safety. Compared with the instantaneous outflow model, the results of the constant outflow model show that the flood storage capacity decreased by 0.05%—0.18%, while the maximum discharge shows the behavior of both increasing and decreasing, indicating that the constant outflow model is not inferior to the instantaneous outflow model. At the same time, the results reveal that the regulation of secondary compensation reduces the flood control storage capacity by 10.6% compared with that obtained with the equal-storage operation model; this result provides a new method for determining the flood control storage capacity of a reservoir.