With the acceleration of urbanization, reservoirs have shifted from single water supply task to multiple tasks, requiring coordination of multiple task competition relationships such as power generation, urban water supply, agricultural irrigation, and river ecology. The scheduling of reservoir engineering realizes planned management, and water allocation work is carried out according to the power generation and water supply plans. To prevent excessive water consumption for power generation, thereby safeguarding the water supply safety for users outside the river, a reservoir optimization operation method based on multiple water use plans is proposed. This method operates through two modes: monthly simulation and monthly optimization. When a water shortage emerges during the monthly simulation, the power generation plan will be readjusted based on the optimization model to ensure the water supply plan of other water users. Taking the optimization scheduling of Qiandao Lake as an example, optimizing the power generation plan in September 2022 led to a reduction of 38.19 million kilowatt-hours. Consequently, the urban water supply in Chun'an County increased by 2.94 million m3, while the monthly storage capacity of the reservoir increased by 216 million m3. This adjustment resulted in a 0.49 m increase in the water level, ensuring the water supply safety for users outside the river. After analyzing the supply–demand balance, the trend of reservoir water level changes, and the monthly distribution pattern of the adjusted power generation plan, it is shown that the proposed calculation method is reasonable and can provide reference for related research.