Due to the large cooling rate, the workpiece often produces thermal stress during the high-pressure gas quenching process, and even plastic deformation or cracking occurs. Therefore, it is particularly important for industrial production to accurately predict the thermal stress distribution of the workpiece during the high-pressure gas quenching process. In this paper, the numerical heat transfer and turbulence model of an exchange flow type vertical high pressure gas quenching furnace was established using computational fluid dynamics method to simulate the gas quenching of a Ti2AlNb hollow workpiece processed by superplastic forming/diffusion bonding.The mesh of simplified furnace model was built using finite volume method and the boundary conditions are set according to the actual working conditions.The simulation results show that at the beginning of gas quenching, the edges around the Ti2AlNb workpiece cool faster than the core. As time increases, the both sides cool faster than the core. The temperature distribution determines the thermal stress distribution. Ti2AlNb workpiece has a high temperature in the core and low temperature at the edges, which causes the core to be restricted by the edges and cannot expand freely, so the core is under compressive stress. During the gas quenching process, the thermal stress does not exceed the yield strength, which belongs to the elastic range.