The high temperature gas such as H2O and CO2 of the exhaust plume of a launching ballistic missile will bring strong IR radiation, so it is the aero heated warhead and the high temperature gas flow around the warhead. The IR radiation is an important signal for IR early warning, tracking and guiding of target in the near-space. The IR radiation characteristics of Angi-Ⅱmissile during launching and reentry stage was studied. Based on narrow band radiation model, and the radiation mechanism of vital gas species were taken into account. The methods for spectral parameters calculation of the species in the high temperature flow were set up, and then a computer code was developed for IR characteristics of targets in the air, which can compute IR characteristics of warhead body and high temperature flow. According to simulated data of the exhaust plume flow and reentry flow around the warhead, the radiation code was used for computing the IR characteristics of Angi-Ⅱ at launching and reentry stage, which can be used as references for early warning and anti-ballistic missile about Angi-Ⅱ.