With the increasing application of multi-port converters in electrical engineering, the design demand for multi-winding transformers is also rapidly rising. The complex electromagnetic parameters and structural optimization of multi-winding transformers have become a significant engineering challenge. Additionally, as the voltage levels of power electronic converters increase, managing the enhanced insulation levels of transformers while addressing the resulting increase in leakage inductance has become another critical issue. This study focuses on a three-winding transformer within a half-bridge LLC topology. Using an iterative approach that combines parameter calculation and software simulation, we optimize the transformer model by adjusting the winding arrangement to balance insulation and leakage inductance. The goal is to enhance the insulation capability of the transformer while achieving balanced leakage inductance between the two equivalent windings of the three-winding transformer. The effectiveness of the calculation method and design scheme is validated through simulation analysis and experimental testing.