Abstract: As a key device in the flexible DC transmission system to achieve a rapid fault removal, the reliability of the hybrid DC circuit breaker directly affects the operation level of the system. Firstly, the multi-state transfer model of the hybrid DC circuit breaker is established by considering the multi-level deterioration state, the maintenance state and the ageing state of the equipment. Afterwards, the basic failure rate is calculated with the reliability block diagram based on the topological analysis. A discretized time-varying failure rate model is obtained combining the health index theory with the Weibull distribution to consider the state differences, while the inspection rate and the maintenance rate are incorporated to obtain the multi-state transfer rate model. The reliability analysis then goes on based on a semi-Markov process. The multi-state reliability index of the hybrid DC circuit breaker is calculated in the context of a certain flexible direct demonstration project, and the sensitivity analysis is carried out on the inspection cycle and the redundancy of each redundant system, the study can provide a strategic reference for the maintenance arrangement and redundancy configuration of hybrid DC circuit breakers.