High Frequency Transformer (HFT), whose main function is power transmission, voltage conversion and electrical isolation, is one of the most important components in Power Electronic Transformer (PET). According to the type-choosing issue of HFT, a design method for HFT applied in PET is given; Considering the high magnetism conductance of nanocrystalline soft magnetic material, a new type of iron-based nanocrystalline is chosen as the core of HFT in this paper. Aiming to the duty ratio loss phenomenon of Phase-shift full bridge DC/DC converter, both the product of area method and the theory of Phase-shift full bridge DC/DC converter are combined to design the HFT; the ratio of HFT is calculated as well as the primary and secondary winding of HFT are programmed. At last, the core loss, alternating-current resistance, winding temperature rise and dielectric strength of HFT are tested and analyzed. It has been shown by the experiments that the design method is effective and feasible.