Airborne target detection in the infrared has been commonly known as infrared search and tracking (IRST), and its detection targets are point source targets. The detection range is an important and systematic indicator of the IRST system, which directly affects the ability and effect of the system to perform tasks and is the important basis for evaluating the system performance. For high-altitude IRST system, the detection range is closely related to the each link in the entire imaging process, such as target, background, atmosphere, optical system, and imaging detector, etc. Starting from the infrared radiation characteristics of the aircraft target and combined the atmospheric transmission, the radiation intensity differences between the target and the background in the mid-wave and long-wave bands were given. Based on the point source target/background signal-to-noise ratio model, the comparison analysis of the mid-wave and long-wave performance was carried out, which had reference significance for the design and analysis of IRST systems.