This paper presents a three-port power electronic transformer (PET) based on high-frequency-link (HFL). Compared with traditional common DC bus based topology, the HFL based topology can reduce power conversion levels. Meanwhile, the electrical isolation among all ports can also be realized. By using the modular multi active bridge (MMAB), which is the basic unit in the PET, the scalability both in voltage and power levels can be guaranteed. The model of a three-port power electronic transformer, including LVAC port, LVDC port and MVDC port, based on HFL is analyzed and the control strategy is proposed. Finally, the three-port PET is verified by simulation and experimental results.