The invention discloses an HBSM (half bridge sub-module) capacitance-voltage balance method for a hybrid MMC (modular multi-level converter). A converter station is formed by mixing a FBSM (Full Bridge Sub-module) and an HBSM. When the proportion of FBSM is lower and a DC system runs at lower voltage, DC bias of bridge arm currents is improved by increasing reactive power on the AC side, so that positive and negative bridge arm currents are present, the charging and discharging probability of the HBSM is increased, and capacitance-voltage balance is controllable.