Abstract: In order to study the radiation characteristic of the high temperature and high velocity exhaust plume sprayed from hypersonic air vehicle, the infrared radiations at 4.3 and 2.7 μm atmospheric window which were emitted from CO₂ and H₂O molecules were measured. The simulated hypersonic exhaust plume jet was generated from hydrogen and oxygen detonation shock wave. The Mach number of exhaust plume was 5.5. Infrared detector in the experiment was the unit type of InSb which was calibrated in situ using standard blackbody. The measurement length was 0.7 m. A single lens and a diaphragm were used to collect the spectrum. Several points in the plume area were measured along the flow direction and the vertical direction respectively, and the corresponding distributions of radiance and spectral radiance were obtained. The final results illuminate that spectral radiance at 4.3 μm was stronger than that at 2.7 μm.