The nuclear reactor power control system is mainly used to control the start-stop of the reactor, power adjustment, and safe operation under accident conditions, and is one of the most important systems for the safe operation of nuclear power plants. In this study, a nonlinear reactor core model is established based on the time–space fractional point reactor model considering the thermo-hydraulic effect. A variable universe fuzzy FOPID controller is designed for a nuclear power control system based on the nonlinear fractional reactor model. The scale factors of the fuzzy inputs are represented by a piecewise function, which simplifies the design process of the variable domain fuzzy controller. The performance of the proposed controller is evaluated with different operation conditions. The simulation results show that the proposed variable universe fuzzy FOPID controller has a smaller overshoot, faster response, and higher control accuracy than the FOPID controller, and has satisfactory ability to the disturbance introduced by the internal parameters uncertain.