Abstract: Taking the gas insulated switch-gear（GIS） bay as the research object, considering the factors of skin effect,contact resistance, natural convection and radiation, etc.Multi-physics field coupling simulation model for 3 D electromagnetic, flow and temperature field of miniaturized GIS bay was established. Power loss, temperature and gas flow distribution of the whole GIS bay were calculated and analysed,and the distribution of the temperature gradient was obtained.Aimed at typical current-carrying structure of miniaturized GIS,a multi-objective and multi-parameter optimization algorithm based on differential evolution algorithm was proposed, and the outer diameter of cylinder can be reduced by 4.7 % and the cost by 22.6 %. The structure was applied to the miniaturized GIS,the temperature-rise test according to China standard had been passed, and the maximum error of the temperature-rise simulation is less than 8%. The accuracy of the simulation model and the rationality of the optimization algorithm are verified. The simulation technology and optimization method provide a good theoretical and technical support for miniaturized GIS current-carrying design and optimization.