This paper took the actual 110 kV high-voltage coaxial GIS as the research object. Its mathematical model and 3D magnetic-thermal coupled finite element model were both established, and then, the electromagnetic field and eddy current field were analyzed. In order to analyze the influence of the shell eddy current loss on GIS thermal distribution, the thermal distributions under the two conditions of taking and not taking the shell eddy current loss were calculated by combining the classical heat transfer theory. The simulation results indicate that the thermal distribution is not uniform because of air convention, and the thermal distribution has the characteristics of bilateral symmetry and from top to below. The highest local temperature rise point is at the top of the GIS busbar. The shell eddy current loss has some effect on the thermal distribution, but the temperature rise difference is in 0.5 ℃. Therefore, the research work can provide important reference for the design and check of high-voltage GIS.