Abstract: The study of boundary layer transition (BLT) is extremely important in the design of high-speed vehicles, and it is currently one of the most popular research topics. The experiments for a HyTRV (Hypersonic Transition Research Vehicle) model under Mach 6 are conducted in a wind tunnel. The effect of surface roughness, angle of attack, and unit Reynolds number on the transition of the HyTRV windward is studied using infrared thermography and numerical simulation. The experimental findings of the same model in two wind tunnels are compared. The results reveal that increasing the surface roughness has less effect on the transition position, with roughness states of 1, 3 and 6 μm. Increasing the angle of attack (within the tested range of 0-6 degrees) effectively suppresses crossflow transition while promoting centerline streamwise vortex transition. Moreover, increasing the unit Reynolds number promotes both crossflow and centerline vortex transition, leading to higher transition Reynolds numbers. Notably, the transition position of the same model varies considerably in different wind tunnels. For the same unit Reynolds number, the transition Reynolds number of the wind tunnel with a large nozzle-exit scale is higher than that of the wind tunnel with a small nozzle-exit scale.