Abstract: The Wudongde-Baihetan-Xiluodu-Xiangjiaba cascade reservoirs in the lower Jingsha River shoulder the downstream flood control tasks jointly, and the complementary equivalent relationship between the flood prevention storage of these reservoirs is not considered during the planning and design stage.Based on the principle of water balance and the assumption of total flood prevention storage unchanged, the flood prevention storage of cascade reservoirs was aggregated and decomposed.The optimal allocation calculation formulas for two-reservoir and multi-reservoir systems were derived and solved numerically with power generation as the main objective.Results show that the Wudongde and Xiangjiaba reservoirs with relatively small storage allocate about 1.180 and 0.216 billion m³ of the flood prevention storage to the Baihetan and Xiluodu reservoirs respectively, which can generate extra 445 and 32 million kW·h hydropower from July to August for the Wudongde-Baihetan and the Xiluodu-Xiangjiaba aggregation systems.Joint and optimal allocation of flood prevention storage for the four cascade reservoirs can increase 1.037 billion kW·h hydropower annually from July to August, yielding significant economic benefits.