The modular multilevel converter (MMC) features high flexibility, scalability, and low voltage distortion, which has become one of the most promising topologies in medium-voltage (MV) applications, especially variable-speed motor drive. While the capacitor voltage ripple would be unbearable during low speeds. The resonant operation of MMC is considered and investigated in this paper to suppress the voltage fluctuation. The method to demonstrate the parameters is also given in this paper.