The invention provides an MMC capacitor voltage-sharing strategy with low switching frequency and complexity. The MMC capacitor voltage-sharing strategy comprises the steps of S1, rapidly monitoring acapacitor voltage value of each sub-module; S2, determining the number of input and removed sub-modules, and judging the charging and discharging conditions of the input sub-modules in the bridge arm; S3, continuing to use the sorting result of the last period, grouping the sub-modules in the input state and the cut-off state to perform insertion sorting correction for limiting the step number, the step number being determined by the maximum voltage difference, and the larger the difference value is, the larger the step number is; S4, according to the charging and discharging conditions, introducing a retention factor to the capacitor voltage of the corresponding sub-module; S5, merging the two sub-sequences in the input state and the cut-off state in two paths, and updating and recordinga sorting result; S6, generating the trigger pulse. According to the invention, dual optimization of the sorting algorithm operation speed and the device switching frequency is realized, and the problems of large sorting algorithm operation amount and high device switching frequency in the traditional sub-module capacitor voltage-sharing strategy are solved.