For a variety of defects of the traditional coupling switch, a flexible coupling switch based on modular multilevel converter topology is proposed. It can connect the networks with different voltage levels, achieve optimal regulation of power flow, reactive power compensation, and emergency support and rapid fault isolation between fault AC system, and meanwhile has DC voltage output port which can be used in AC and DC power distribution networks. The operating mode of the flexible coupling switch is analyzed, and DC voltage and power flow controller are designed. Finally, simulation and experiment results verify the performance of the switch. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 52466F160002).