Abstract: Compared with traditional flexible DC transmission systems, the modular multi-level converter-based multi-terminal high voltage direct current (MMC-MTDC) system has a larger number of factor modules, a more complex structure, and more operating states, making its reliability modeling more challenging. This article proposes a Monte Carlo analysis method for the reliability of MMC-MTDC considering module redundancy and system state. Firstly, based on the reliability block diagram method, a reliability model for converter valves considering module redundancy was established, and a reliability model for converter stations considering the influence of multiple devices was further constructed. Secondly, based on the analysis of the actual multi-state transition process, an MMC-MTDC probability density model considering the duration of state transition was established, and a Monte Carlo-based reliability model solution method for MMC-MTDC was proposed. Finally, taking an actual ±200kV MMC-MTDC system as an example, the reliability indicators such as state probability, state duration, and state frequency under multiple operating modes were solved. The study can provide some reference for the reliability analysis of MMC-MTDC.