The invention belongs to the field of power electronic technology and DC power transmission, and particularly provides a capacitor voltage balance control method for a full-bridge MMC (Modular Multilevel Converter). First, the number of sub modules needing to be switched on is calculated for each bridge arm of a full-bridge MMC, and different sub modules are selected for next operation according to different numbers; then, a capacitor voltage sorting method is selected according to whether the maximum capacitor voltage difference of the sub modules exceed a set limit; and finally, full-bridge sub modules needing to be switched on or cut off are decided according to the difference in number of sub modules needing to be switched on in two consecutive control periods and the current directions of the bridge arms. According to the invention, capacitor voltage balance control on the sub modules of an MMC topology can be realized in a dynamic process, and energy can be evenly distributed in the whole converter.