The invention relates to a sub-module capacitive voltage equalization control method for a modular multilevel converter, which belongs to the technical field of voltage source converters and the technical field of direct current transmission. The method provided by the invention comprises the steps that currently input sub-module capacitive voltage in a bridge arm and cut sub-module capacitive voltage are sorted; and according to the direction of the bridge arm current, the difference between the number of sub-modules to be input at the current moment and the number of sub-modules to be input at the previous moment, and the capacitive voltage sorting result, the number of input and cut sub-modules is controlled to realize the effect of sub-module capacitive voltage equalization. Compared with a conventional capacitive voltage value sorting method, the method proposed by the invention has the advantages that unnecessary sub-module switching is reduced; the switching frequency is reduced; and the switch loss is reduced. According to the invention, independent selection of the sub-module switching frequency according to actual engineering requirements is realized; the flexibility is greatly increased; as the number of sub-modules on the bridge arm increases, the advantages of the method become more and more obvious; and the method is suitable for modular multi-level converters with large levels.