Abstract: Joint flood control operation of reservoirs is an important technical measure to improve flood control safety of the river basin. During the flood control operation, water imbalance is usually caused by the flow travel time in the upper and lower reservoirs in a cascade reservoir system. It is of great significance to study the flow delay in that system and propose an effective measure for flood control operation. This study proposes a real-time flood control joint operation method to address the influence of water flow delays, applying information value maximization for cascade reservoirs under the condition of “weak coupling.” The excess water consumption mechanism is established from the lowest reservoir to the uppermost one. Based on this mechanism, a compensation operation model is established based on the maximum peak shaving principle, which minimizes peak flow on flood control cross-section, utilizing the hydrological and hydraulic compensation function in cascade reservoirs. This paper takes the northern tributary of the Beiliao River Basin of Jiangxi Province with three cascade reservoirs as a case study, whose results of the multi-scenario simulation show the following message. Considering the hydraulic engineering and flood characteristics of the area, during small and medium floods, the regulation function of each reservoir can be appropriately exploited to grasp the initiative of flood control. During large flood events, the flow should be pre-discharged to a lower water level to ensure that the reservoir group has sufficient flood control capacity. It can fully use the reservoir group’s flood control function in the basin and relieve downstream flood pressure to the greatest extent. After the operation mentioned above, the average ratio of cutting down flood peak of Luowan Reservoir is 20.63%, with a detention volume of 496 thousand cubic meters. The average ratio of cutting down flood peak of Hongping Reservoir is 30.09%, with a detention volume of 13.95 million cubic meters. The average ratio of cutting down flood peak of Xiaowan reservoir is 33.02%, with a detention volume of 5.97 million cubic meters. Peak flow at the flood control cross-section decreases by 48.83% on average compared to the peak flow of natural inflow. The peak reduction effect of the joint flood control operation of reservoirs is more significant than the original scheduling rules in the area.