Abstract: The power of the submodules in the modular multilevel converter-battery energy storage system (MMC-BESS) fluctuates periodically. The charging and discharging states of the connected battery packs switch frequently, resulting in extra charge throughput and endangering their lifespans. In the medium-voltage DC (MVDC) distribution network, the AC and DC power transmission of the MMC-BESS is complicated and variable, which further increases the difficulty of suppressing the charge throughput. Therefore, a charge throughput suppression strategy based on second-order circulating current injection is proposed for the MMC-BESS in the MVDC distribution network. Firstly, the mathematical model of the MMC-BESS is established in the MVDC distribution network. Secondly, the generation mechanism of the charge throughput of the MMC-BESS is analyzed, and the influencing factors of the charge throughput under different operating modes are analyzed. Furthermore, a charge throughput suppression strategy based on second-order circulating current injection is proposed. By minimizing the total charge throughput of the system, the optimal second-order frequency components of the circulating currents are selected under different working conditions. Finally, simulation and experimental results under various working conditions show that the proposed method can effectively suppress the charge throughput of the MMC-BESS in the MVDC distribution network.