Abstract: To protect fish reproduction, hydropower stations in the upper reaches of Yellow River are required to implement ecological dispatching that simulates natural hydrological regimes during specific seasons, which limits their peak shaving capacity. Taking the Maerdang hydro-wind-solar-storage base as the research object, this paper investigated a peak shaving mode that took the reservoir of run-of-river conventional hydropower station as the lower reservoir to build a pumped storage power station. A joint operation model for the hydro-wind-solar-storage system was constructed to quantitatively evaluate the impact of different pumped storage capacities on peak shaving performance and reservoir water levels. The results indicated that the configuration of a pumped storage power station can effectively balance renewable energy fluctuations. Increasing the pumped storage installed capacity (from 1 800 MW to 4 200 MW) reduced the system′s residual load fluctuation by 40.1%. However, the average daily maximum water level fluctuation of the conventional reservoir increased by 174.17%, and the maximum water level ramp rate increased by 60. 82%. This study quantitatively revealed the trade-off between peak shaving benefits and water level disturbances and proposed a coordinated peak shaving strategy under ecological constraints. The conventional hydropower station maintained run-of-river operation, the pumped storage station undertook peak shaving tasks, and ecological red lines were established for reservoir water level fluctuations to balance peak shaving demands with ecological protection.