Abstract: The high-power high-frequency transformer is the core component of power electronic transformers, which are widely demanded in future new grid connection, offshore wind power, medium-voltage distribution networks, rail transit and data center power supply. This article provides an overview of the key issues and development trends in the research on high-power high-frequency transformers. The current situation of materials, losses, structural design and manufacture of high-power high-frequency iron cores have also been discussed in the article. Some key issues related to high-power high-frequency iron cores and windings are addressed as well after overviewing the material and structural development on the current basis. The discussion focuses on the high-frequency high-voltage insulation and heat management system, as well as the conflicting issues in designing the insulation failure, reliability and heat dissipation. The design method of high power density is put forward, and the insulation system, temperature rise, and efficiency tests are also proposed through a review of the current status of the design, tests, and techniques. The key issues and development trends in high-power electronic transformers are finally discussed.