Abstract: As a key hub device of AC-DC hybrid distribution system, multi-port power electronic transformer has the functions of bidirectional energy flow, flexible power flow regulation, harmonic and reactive power control and fault isolation, which has attracted more and more attention in recent years. Targeted at the multi-port power electronic transformer oriented for AC/DC hybrid distribution system, this paper deduces the development process of its topological structure. From the perspective of graph theory, the star-type and the series-type structures are catalogued. From the form of the energy pooling part, the common DC-bus structure and high-frequency-coupling structure are summed up. Then, the advantages and disadvantages of different topological structures are compared and analyzed, and the principle of selecting topologies for different practical requirements of AC-DC hybrid distribution system is provided. Furthermore, this paper summarizes the application challenges of multi-port power electronic transformer in simulation, design, control and protection, and its prospects in future technical development are provided.