The possible application of the film-cooling technique against aero-thermal heating for surfaces of high-speed flying vehicles is discussed.The technique has been widely used in the heat protection of gas turbine blades.It is shown in this paper that,by applying this technique to high-speed flying vehicles,the working principle is fundamentally different.Numerical simulations for two model problems are performed to support the argument.Besides the heat protection,the appreciable drag reduction is found to be another favorable effect.For the second model problem,i.e.,the gas cooling for an optical window on a sphere cone,the hydrodynamic instability of the film is studied by the linear stability analysis to observe possible occurrence of laminar-turbulent transition. The possible application of the film-cooling technique against aero-thermal heating for surfaces of high-speed flying vehicles is discussed. The technique has been widely used in the heat protection of gas turbine blades. It is shown in this paper that, by applying this technique to high-speed flying vehicles, the working principle is fundamentally different. Numerical simulations for two model problems are performed to support the argument .esides the heat protection, the appreciable drag reduction is found to be another favorable effect. For the second model problem, ie, the gas cooling for an optical window on a sphere cone, the hydrodynamic instability of the film is studied by the linear stability analysis to observe possible occurrence of laminar-turbulent transition.