Modular multi-level converter based solid-state transformer (MMC-SST) has gained wide attention in AC-DC hybrid distribution network due to the availability of ports with multiple voltage levels and voltage patterns. Dual active bridge (DAB)-type MMC-SST has problems such as low power density and high cost,and the tradition-al half bridge structure of DAB-type MMC-SST has failure to clear fault current in case of short-circuit faults at me-dium voltage direct current (MVDC) ports,which affects its application in distribution network. Although full bridge structure of DAB-type MMC-SST has fault blocking capability,it also increases the number of switches. Improve the topology of the traditional DAB-type MMC-SST,then a clamped switch pair integrated submodule (CSPI)-type MMC-SST topology is proposed based on the principle of frequency mixing modulation. The proposed topology not only reduces the number of switching devices but also makes the SST have the capability of clearing MVDC short-circuit faults,as compared to the traditional half bridge and full bridge DAB-type MMC-SST topologies. The power density and power supply reliability of the DAB-type MMC-SST are greatly improved by the proposed topology. The feasibility of the proposed CSPI-type MMC-SST topology and frequency decoupling method is verified through theoretical analysis and simulation.