The load current and shell edgy of GIB will incur equipment heat during the operational process and its feature of temperature rise is an important indicator of operating state of the characterization GIB. Based on the principle of heat transfer and hot analogy method, the heat transfer process in 126 kV/2 kA three-phase enclosed GIS bus bar is equivalent to a simple thermal circuit of lumped parameter, considering the heat capacity of the conductors, the coefficient of heat transfer and nonlinear thermal resistance between the conductor and the tank respectively with the SF6 gas, and the equivalent thermal circuit model of three-phase enclosed GIS bus bar is established in this paper. The temperature measurement experiment of three-phase enclosed GIS bus bar is designed, the model’s calculation results are compared with the experimental results, and the accuracy and effectiveness of the dynamic thermal-circuit model is verified, and obtained the corresponding temperature rise curves between the shell and the conductor by the thermal circuit model.