Gas insulated switchgear (GIS) is one of the most important equipment in the power system. Excessive temperature of the GIS busbar conductor will lead to the loss of insulating gas performance and equipment life. In the present paper, based on the finite element method, the temperature distribution and power loss density of a 252 kV three-phase GIS busbar is numerically studied using electromagnetic-heat-flow coupling model, and the structure parameters of the rotation angle, center distance and conductor thickness of the busbar are optimized with Taguchi method. The results show that the conductor thickness has the greatest influence on the maximum temperature and power loss, and the influence proportion is more than 70 %. When the combination scheme of (A1, B5, C5) is adopted, the temperature rises and power loss performance of GIS has been optimized. The maximum temperature is reduced by 9.56 K and the power loss is reduced by 21.7 %. In addition, according to the analysis of the gas breakdown margin, it is found that the SF6 gas still has a good insulation performance after structure optimization. This study is of great significance to the heat transfer and optimization design of three-phase GIS busbar.