Abstract: The control rod drive mechanism is the servo mechanism of the reactor control and protection system. It is an important nuclear safety equipment for performing reactor power regulation and emergency shutdown. The cost of the control rod drive mechanism is high, and how to determine the number of spare parts is important for improving the operability of the reactor. In this paper, for the control rod drive mechanism, under the constraint condition that the continuous operation time of the system is not less than the refueling cycle, an optimization method for determining the number of spare parts for the control rod drive mechanism, the optimization method of grouping spare parts quantity, was proposed. And the spare parts configuration scheme of each subsystem with the least total cost was given. By the stochastic simulation calculation, the method of optimizing the number of spare parts was compared with the conventional algorithm. The results show that the optimization method is better than the conventional algorithm. Under the premise of ensuring the availability of the control rod drive mechanism, optimizing the number of spare parts can reduce the cost. The optimization method is also applicable to the analysis of spare parts of other equipment, and has guiding significance for the analysis and research of equipment spare parts in engineering.