With the increasing popularity of renewable energy and the rapid development of power semiconductor technology,the application of solid-state transformer will be more widely used. Solid-state transformer increases operating frequency which can significantly reduce the volume and weight of magnetic components. The resonant converter which is made by the seniors of laboratory is reviewed in this paper. The 10 kVA cast resin transformer of the resonant converter is reviewed and analyzed. Then,larger power cast resin transformer is carried out. This paper mainly focuses on the parameter design and insulation considerations of the 40kVA high frequency cast resin transformers,and uses the software COMSOL Multiphysics® to simulate. Finally,the transformer is adopted into the resonant converter to verify its feasibility,and the resonant converter is tested under input 2600 Vdc and output 400 Vdc.