This chapter proposes a three-port medium-voltage flexible switch to solve the problem that traditional medium-voltage flexible switches can only connect two ports. The device adopts a modular cascaded topology structure. The power module is divided into three groups, which are used to connect the A-phase, B-phase, and C-phase of three medium-voltage AC ports. Each power module group contains multiple power modules inside. Each power module has three line-frequency single-phase AC ports. These three communication ports are electrically isolated from each other. Power can flow from any one (or two) port to the other two (or one) ports. This flexible switch realizes flexible interconnection between three medium-voltage distribution power grids, and the power value and direction between any two medium-voltage distribution power grids can be independently controlled. Compared with traditional solutions, it uses fewer components, resulting in a smaller volume and lower cost.