The invention discloses a zero DC voltage fault ride-through control method of a multilevel modular converter (MMC) under an asymmetric state of bridge arm parameters. Sub-modules in the MMC all employ full-bridge sub-modules, an auxiliary loop is added among bridge arms of the same DC bus side to build a new topology, energy equalization of three upper bridge arms and energy equalization of three lower bridge arms are maintained when the auxiliary circuit among the bridge arm works during the zero DC voltage fault ride-through process, all modular voltages are integratedly equalized by adjusting voltage deviation among the upper bridge arms and the lower bridge arms, a fault current is enabled to be eliminated during the zero DC voltage fault ride-through process of the MMC, reactive power support is continued to be provided for an AC system, and the energy equalization of the sub-modules is maintained particularly when the bridge arm parameters of the MMC are asymmetric. By the topology and the control method thereof, the voltage deviation caused by asymmetric bridge arm parameters can be jointly borne by the six bridge arms, the integral energy equalization is maintained, a short-circuit current is limited to a low level, and zero DC voltage fault ride-through is achieved.