This paper mainly focus on the design and implementation methods of a 150kW high power high frequency transformer (HPHFT) in high voltage solid state transformer consist of multi-DABs (Dual Active Bridges). Based on theoretical analysis and design experience, the detailed calculation process of winding loss considering skin effect and proximity effect is given and also the loss calculation method of nancrystalline materials. Then some other aspects of the design process, such as winding structure, insulation and so on, are introduced. At last, a prototype of a 150kW high frequency transformer was implemented, experimental results of the proposed transformer coincide with the design.