The optimization method of winding structure parameters of oil-immersed transformer is proposed to reduce the hot spot temperature of transformer and the metal conductor consumption based on the coupling calculation method of electromagnetic-fluid-thermal. Firstly, according to the electrical and structural parameters of the oil-immersed transformer, a 3D simulation model is established by using finite element software, and the distribution of the thermal field and the fluid field around the transformer as well as the fluid field and thermal field of the low-voltage winding are obtained. In order to accurately reflect the temperature rise distribution characteristics of the low-voltage winding, a 2D model of the low-voltage winding of the transformer was established considering the calculation efficiency and accuracy, and the thermal field and fluid field distribution of the two low-voltage winding models were compared and analyzed. The temperature error was less than 5.98℃, which verified the accuracy of the equivalent model. On this basis, the hot spot temperature of low voltage winding under different structural parameters is obtained by combining the Latin hypercube experiment design and thermal field simulation method, and the response surface model of winding hot spot temperature and structural parameters is established. Taking the hot spot temperature of low voltage winding and the amount of metal conductor as optimization objectives, combined with the response surface model, the optimal solution set of Pareto is obtained by using NSGS-Ⅱ optimization algorithm, and two kinds of optimal design results are obtained on the Pareto front surface. The results show that the hot spot temperature is reduced by 4.16% and the metal conductor consumption is reduced by 13.79% in scheme 1; the hot spot temperature is reduced by 0.51% and the metal conductor consumption is reduced by 28.46% in scheme 2. The research results have important guiding significance for the optimization of oil-immersed transformer.