Abstract: While high-speed aircraft are flying in the atmosphere, its optical-hood is subjected to severe aerodynamic heating. The supersonic gaseous film cooling method can effectively isolate the external heating, but the mixed layer formed by the cooling gas and main stream can cause the beam degradation and affect the imaging quality. To reduce the beam degradation and improve the supersonic gaseous film cooling optical performance, based on the simultaneous matching of refractive index and pressure, two design methods were proposed, respectively, which configured the specific cooling gas temperature to achieve the mixed layer refractive index and pressure matching at the same time, and configured the specific cooling gas component to achieve the mixed layer refractive index and pressure matching at the same time. The feasibility and effectiveness of these two methods were verified. The simulation prove that, for the latter method, the mass ratio of the cooling gas is related to the static temperature of the cooling gas only without the changing of the external flow parameters, which is the basis for the synchronous design of cooling and optical performances of the gaseous film.