The invention discloses a multi-port power electronic transformer of a mixed cascading structure. The power electronic transformer comprises a rectification grade and intermediate isolation grades. The rectification grade is formed by cascading M mixed cascading modules, the mixed cascading modules comprise H-bridge rectification modules and n submodules, the input ends of the H-bridge rectification modules are connected with a power network after being cascaded, the output ends of the H-bridge rectification modules are connected with the input end of a module formed when the n submodules are connected in series, and the output ends of M*n submodules are respectively connected with the input ends of respective isolation modules; and the output ports of the M*n isolation modules are taken as the DC output ports of the power electronic transformer, and the DC output ports are connected in series and in parallel according to a needed voltage grade and a needed output capacity. The multi-port power electronic transformer is especially suitable for application in conversion from a high-voltage occasion to a multiport low-voltage occasion; under the condition that the quantity of DC ends is the same, the device quantity is reduced, and the cost is substantially decreased; and a full modular structure enables the capacity expansibility to be good.