Abstract: Phase change auxiliary cooling is an economical and effective way to improve the overload capacity of a transformer. In view of this new transformer topology, thea temperature calculation method was proposed by combining the field analysis and the thermal circuit model. Firstly, the lumped parameter thermal circuit model of the phase change auxiliary cooling distribution transformer was established, and the method of obtaining the contact thermal resistance between auxiliary cooling module and corrugated fin was studied by using thermal circuit equivalent temperature node combined with heat dissipation experiment of cooling module was studied. Based on the thermal circuit model, the overload operation performance of transformer under various complex load conditions was predicted and evaluated, which can provided reference for the safe overload operation strategy of the transformer. In the three-dimensional fluid structure coupling model of the field analysis method, the equivalent convective heat transfer coefficient of the thermal circuit was set at the contact surface between corrugated fin and cooling module. The boundary conditions were provided by the thermal circuit model, and the temperature field and flow field distribution were obtained by using the finite volume method. Through the comparison of prototype experiments, it iscan be found that the maximum relative error between the calculated results and the experimental results of hot spot temperature and top oil temperature are less than 10%, indicating that this method can meet the requirements of engineering calculation.