To solve the dispatching problem of water-light complementary base, a new drawing method of reservoir dispatching diagram is proposed according to the frequency group of incoming water, and the application strategy of reservoir dispatching diagram is provided. Taking the Xizang section of the upper reaches of Lancang River as an example, the results obtained by the proposed method meet the practical requirements of the project, benefit the stable operation of the power grid, and improve the efficiency of the power station.