In order to save water, reduce expense and improve economic benefit, based on operations research theory,the paper applied continuous random storage model to water dispatching so as to optimize the storage of reservoir water and make full use of water. The analysis of example indicated that this model is reasonable in application of water dispatching system. The value of Q is gotten by calculating and limiting, the expectation of water loss is the minimum. The results can provide reference for the water dispatching of reservoir, the water storage of productive enterprise and the allocation of every water user.