Many factors can affect long range detection of infrared system,such as the characteristics of the moving point target,background radiation,near field optical radiation,the performance of detector.Starting from the basic principle of point target detection,taking detecting the extraatmospheric moving target under deep space for example,estimation model of infrared detection range of long range target is established.Some influence factors on detection range are analyzed,which can provide a theoretical reference for design of long range infrared system.