Based on the thermoelectric analogy theory and the principle of heat transfer, a GIS coaxial bus thermal network simulation model is established by comprehensively considering the skin effect, resistance temperature coefficient, heat conduction, heat convection and heat radiation. The temperature rise of the bus conductor and the shell under different inflation pressures was obtained by calculation, which took about 5s. The real prototype was built and the temperature rise test was carried out. The comparison results between simulation and test show that the conductor error is 3.36% and the shell error is 6.85% under the inflation pressure of 0.43Mpa. At 0.5Mpa, the conductor error is 2.60% and the shell error is 7.18%. The rationality of the method and the accuracy of the results are proved.