When high-speed tandem layout vehicle reaches predetermined separation point, payloads needs to separate from the booster, in order to separate successfully, it is feasible to apply jet thruster on the booster to provide reverse thrust, thus makes the booster separate safely from the payloads. During this stage separation, high-temperature gas ejected from jet thruster not only generates strong infrared radiation, but also affect the temperature distribution on vehicle’s surface, which ultimately affects the radiation characteristics of the target. Meanwhile, due to the high flight speed, inflow air and jet gas in flow field will be involved in complex chemical reactions such as dissociation, ionization and afterburning, which can also significantly affect the radiation characteristics of the target. In the field of aircraft detecting and tracking, most researches focuses on aircraft’s steady state infrared radiation characteristics, while the transient radiation characteristic during the stage separation is a typical characteristic different from those steady state characteristics, investigation on this transient radiation characteristic can provide useful reference for aircraft detecting and tracking application. This paper investigates the influence of high-speed aircraft’s stage separation on target infrared radiation characteristics, the infrared radiation characteristics of flow field and aircraft’s surface is analyzed, the influence of jet gas’s chemical reaction, observation wave bands and observation angles on radiation characteristics is also studied.Typical lifting body payload with booster is used as research object (Fig.3), three-dimensional Navier-Stokes equation with chemical reaction source term is solved to simulate the high-speed aircraft’s stage separation flow field, the chemical reactions of jet gas and inflow air is considered. By using radiative equilibrium wall condition, vehicle’s surface temperature is calculated. The radiative transfer equations are solved based on statistical narrow band model and apparent light method. A Cartesian coordinate system is used to describe the radiation distribution, the observed angles are represented by zenith angle θ and circumferential angle φ (Fig.8).During the stage separation, infrared radiation sources include the infrared radiation from the vehicle’s high temperature wall, and the infrared radiation from the high temperature gas components in flow field, however, the infrared radiation intensity of them is roughly in the same order of magnitude (Fig.9). Infrared radiation of flow field is mainly contributed by CO₂ and H₂O, the contribution of other components is relatively small, spectral radiation curve has two obvious peaks of 2.7 μm and 4.3 μm (Fig.10). When jet thruster on booster stage works, compared with jet off condition, the target infrared radiation intensity of aircraft increases significantly, the radiation intensity can be increased several times at specific wave band and detection angle (Fig.11). The infrared radiation intensity of upside observation is slightly higher than that of downside observation (Fig.11), which is due to the existence of flight angle of attack and the wall temperature in windward region is higher than that of leeward region (Fig.7). The radiation intensity of 1~3 μm band is the largest, which can reach 2~3 times of other bands under specific detection angle (Fig.11), this is because the peak value of infrared radiation generated by wall is near the wavelength of 1 μm (Fig.9), while the radiation generated by the flow field is mainly contributed by H₂O and CO₂, whose infrared radiation peak are also near the wavelength of 1~3 μm (Fig.10). When considering the chemical reactions of jet gas, the target infrared radiation intensity of aircraft can drop up to 50% at specific wave band and detection angle (Fig.11), this is because the high flight altitude and low inflow oxygen density, afterburning reaction is weak, and due to the high flight speed and high temperature in the shock layer, jet gas components mainly involves in dissociation reaction, which makes flow field temperature and the mass fraction of H₂O and CO₂ drops (Fig.12, Fig.13), thus makes the target infrared radiation intensity drops significantly.During the high-speed aircraft’s stage separation, infrared radiation intensity of flow field and aircraft’s surface are almost in the same order of magnitude, infrared radiation in flow field is mainly contributed by CO₂ and H₂O; The radiance enhancement caused by jet gas is significant, target radiation intensity can increase up to several times, the radiation intensity at 1~3 μm band is the strongest; Due to high flight speed, jet gas components mainly involve in dissociation reaction, which makes flow field infrared radiation intensity drop up to 50%, and this is different from the situation in low altitude where the jet gas’s afterburning effect can make flow field infrared radiation intensity increase significantly.