Abstract: Clarifying the influences of the water-sediment regulation and the west route of the South-North Water Transfer Project on the reservoir capacity of the cascade reservoirs at the upper Yellow River in the future, and exploring the reasonable benefical reservoir capacity of the cascade reservoirs in case of the comprehensive water consumption, and in consideration of the comprehensive demands of water supply in the Lanzhou section, power generation and water-sediment regulation by the cascade reservoirs, flood control and ice flood protection, a joint operation model for cascade reservoirs considering the minimization of water deficiencies is developed with eight schemes for the current and prospective years. The self iterative simulation optimization algorithm is used to solve the model, and the long series runoff data are applied to optimize the operation calculation. The time series method is used to deduce the benefical reservoir capacity of the cascade reservoirs and determine the reasonable capacity of the cascade reservoirs. The benefits of the water-sediment regulation, power supply and power generation are quantified according to the frequency of the water and sediment regulation, average annual water supply quantity, guarantee rate of water supply, and average annual energy output and power generating guarantee rate. The analysis results show that the reasonable reservoir capacity of the cascade reservoirs will increase with the increase of comprehensive water demand and the water-sediment regulation frequency, and that the implementation of the west route of the South-North Water Transfer Project will help to reduce the scale of the reasonable capacity. Only eighth of the sediment regulation schemes show that the beneficial reservoir capacity of the cascade reservoirs can meet the comprehensive water demand, and that reducing the intensity and frequency of the water-sediment regulation may be a compromise to solve this problem. The research results can provide a scientific reference for the overall layout of the upper reaches of the Yellow River in the future.