Abstract: Based on the grid demand and the construction cost, this paper chooses the proper control manner of the reactor power, and the functional requirement of the operation mode. The operation mode, the control system and load rejection are designed. Finally, the core power capability and relevant accidents are analyzed for the nuclear power plants adopting this operation mode. The results show that the nuclear power plants that adopt this operation mode is safe. The paper introduces the design process of ACP600 operation mode, and it proves that the design method of the operation mode introduced in this paper is correct and practical.