Inside press-pack devices, protective gas is hermetically sealed to improve the insulation strength and prevent electrodes from being degraded due to oxidation. In order to clarify the convective heat transfer characteristics of different protective gas in press-pack power devices, this paper takes press-pack IEGT as an example, analyzes its power losses, and carries out iterative thermal numerical simulation in ANSYS. By comparing temperature distribution of SF₆, N₂, and SF₆/N₂ mixture, Grasof number and Nusselt number are obtained. Then the heat dissipation effect of the three different protective gas is confirmed. This paper provides a reference for the selection of internal protective gas, heat dissipation design and optimization of internal structure of press-pack power devices.