Abstract: The water/electricity cogeneration system of nuclear power plants is investigated in this paper. By coupling the nuclear power plant with large-scale reverse osmosis seawater desalination devices, the system can improve the peak shaving capacity of nuclear power plants and alleviate the water shortage in coastal cities. Through the analysis on peak shaving operation modes for the water/electricity cogeneration system of nuclear power plants, it is concluded that it is desirable for the reverse osmosis desalination devices to be operated at “12-1-10-1” (50% load by day and 100% load by night) variable load mode when the nuclear power units are under the full loading conditions. In this way, the peak shaving capacity of the water/electricity cogeneration system is 33% with the desalination cost of 3.62 Yuan/m³ and the peak shaving cost of 63 Yuan/MWh, indicating the promising future of the system application.