Abstract: With a view on the application of air film cooling in the form of discrete holes in hypersonic vehicle thermal protection, and in order to further understand the structural characteristics of supersonic air film cooling flow field and the coupling mechanism of shock waves on air film cooling, a 3D compressible RANS numerical simulation method was used to investigate the flow and heat transfer characteristics of air film cooling under different mainstream Mach numbers. The results show that, under mainstream supersonic conditions, the obstruction effect of the cooling jet causes shock waves to appear upstream of air film cooling holes, and the intensity of shock waves increases with the increase of mainstream Mach numbers. The shock wave induces the mainstream to deflect along the spanwise direction and move away from the central region of the air film cooling hole. Thus, the interaction between the mainstream and the cooling jet is weakened, and the mixing and dissipating strength of the cooling jet in the spanwise direction is reduced. Therefore, the coverage effect is better and the distance is longer for the air film cooling under supersonic mainstream conditions. In addition, the overall air film cooling efficiency increases with the increase of the mainstream Mach numbers.