As a key device in flexible DC distribution system, the modular multilevel converter (MMC) is directly related to the security and reliability of the whole power distribution system, so it is necessary to evaluate its reliability. In this paper, half, full bridge and mixed MMC are compared and analyzed, and the mixed MMC is more suitable for flexible direct distribution system. The full and half bridge module number and proportion is calculated through the MMC working principle, DC blocking capacity, redundant configuration. The component reliability modeling is established and the fault tree method is used to model the reliability of hybrid MMC. MATLAB is used to analyze the redundancy configuration, full and half bridge sub-module ratio, IGBT junction temperature and loss, and the conclusion is drawn that reasonable redundancy configuration and full and half bridge ratio are the key to the design of hybrid MMC. It is also pointed out that the operation condition of IGBT will lead to the increase of the failure rate of hybrid MMC.