The operation of Fluoride salt-cooled High-temperature Reactors (FHRs) involves complex multi-physics coupled processes, posing significant challenges to the reliability and fault tolerance of the control system. This paper proposes a fault-tolerant control method based on a full-dimensional state observer for real-time fault detection and isolation of the FHR’s nuclear power detectors. The method diagnoses detector faults by comparing the estimated values from the state observer with the measured values from the detectors and adopts appropriate fault-tolerant control strategies based on the fault information. Simulation results demonstrate that the proposed fault-tolerant control method can effectively cope with various typical faults of nuclear power detectors, ensuring the safety and reliability of FHR operation.