Abstract: Molten fluoride is used as the fuel in liquid molten salt reactors. The outlet temperature of the molten salt is an important index to measure the safety of the molten salt reactor. The control of the molten salt outlet temperature can be realized by core power control. The core of the liquid molten salt reactor is divided into inner and outer regions. Based on the principle of energy conservation, the core non-linear model is established, and the non-linear model is linearized by perturbation theory. Based on the core linearization model, the core power control system is designed by using the fuzzy-PID controller. Taking Molten Salt Breeder Reactor(MSBR)of molten salt breeder reactor as an example, core power control simulation is carried out. The results show that when the step reactivity of 10-3 and 2×10-3 is introduced, the fuzzy-PID controller can reduce the amplitude and overshoot of the system response. and the load of the reactor core power changes greatly, the fuzzy-PID controller can track the change of the reactor core power well. Therefore, the fuzzy PID controller has good dynamic performance and can achieve good control of the reactor core power.