Considering the factors of skin effect, contact resistance, natural convection and radiation, etc., Multi-physics field coupling simulation model for 3D electromagnetic, flow and temperature field of AC high voltage GIS busbar is established, power loss, temperature and gas flow distribution is calculated and analyzed, the distribution of the temperature gradient is obtained; Based on the proposed model, calculate the power losses of typical contact structure, effects of contact number, contact spacing and contact position are investigated. The temperature-rise test according to China Standard has been passed, and the maximum error of the temperature-rise simulation is less than 5 %. The accuracy of the simulation model is verified. The simulation technology provides a good theoretical and technical support for AC high voltage GIS busbar current-carrying design and optimization.