Reliability analysis of VSC-HVDC is the premise of safe and stable operation of power system. Firstly, based on the analysis of MMC structure, an MMC reliability model considering subcomponent fault parameters was constructed; Secondly, based on the actual operation mode of the five-terminal VSC-HVDC, a multi-state transfer model is established. Aiming at the problem that the distribution of state transfer time is limited in the traditional Markov process, a semi-Markov based reliability solution method for the five-terminal VSC-HVDC is established; Finally, taking Zhoushan five-terminal VSC-HVDC as an example, the reliability of MMC is analyzed, and the steady-state probability, average unconditional dwell time and other indicators of the system are solved, which can provide some data basis for the reliability analysis of VSC-HVDC.