Abstract: Extending and utilizing the long-period and large-scale regulation capability of hydropower is essential to enhance the level of grid seasonal supply guarantee and wind-solar consumption. The core challenge lies in defining the control range of water levels at key time nodes of leading hydropower stations on a long-term scale. In this paper, a scenario set of runoff-wind-solar power generation capacity combinations considering spatio-temporal correlation is taken as input, and a long-term multi-objective stochastic optimal scheduling model for cascade hydropower stations is constructed to guarantee grid power supply and wind-solar consumption. Taking the Lancang River hydropower base in Yunnan Province as an application example, the water level control intervals of Xiaowan and Nuozhadu two backbone hydropower stations that fulfill the demand of grid supply and consumption regulation are effectively defined. The variation patterns of these hydropower stations are analyzed under different runoff and wind-solar proportions. The results demonstrate that the validity of the water level control intervals exceeds 95%, which can support the grid developing a long-term water level operation plan for the leading hydropower stations. Additionally, as the proportion of new energy increases, the flexibility of hydropower to support new energy regulation has been weakened.