The invention relates to a submodule topology and an MMC converter. At least one submodule in the MMC converter is composed of six switch modules and four capacitors; the submodule topology can achieve the first mode of conducting direct-current fault ride-through in a blocking mode and the second mode of conducting direct-current fault ride-through in a nonblocking mode, and therefore when a direct current fault occurs, the submodules are high in fault ride-through reliability, and a corresponding direct-current fault ride-through mode can be selected according to the actual control need. In addition, under the same voltage level, that is to say, under the same number of a level, the number of the needed switch devices is smaller compared with that of a full-bridge submodule, the cost of a direct-current power transmission project can be effectively lowered, and when the voltage level is higher and the output level number is higher, more switch devices are saved.