The modular multilevel converter based solid-state transformer (MMC-SST) is a crucial piece of equipment for enabling flexible interconnection and multi-directional energy flow in hybrid AC/DC distribution networks. There is a problem of excessive capacitor ripple voltage in the input stage MMC submodule leading to an increase in device size and cost. Thus an improved ripple voltage suppression strategy based on proportional repetitive control (PRC) for the MMC-SST is proposed. First, the adjusted phase shift angle of power is obtained using a capacitor voltage closed-loop based on PRC. Then, the ripple power of the submodule capacitor is transmitted to the low-voltage DC bus through a dual active bridge converter (DAB), effectively suppressing the ripple voltage of the MMC submodule at various frequencies and achieving the goal of reducing the capacitance value. Finally, simulation shows that MMC-SST submodule capacitor ripple voltage suppression strategy based on PRC has good ripple voltage suppression ability in conditions of symmetrical or asymmetrical grid side voltage.