The infrared radiation characteristics of the environment for spacecraft play a significant role in the infrared characteristics of the spacecraft. Thus the study on infrared radiation of aircraft background is essential. The regime which only consists of the regional atmospheric climate system in the field is called limb background in the view of the atmosphere system of the earth. Based on moderate spectral resolution atmospheric radiation transmittance algorithm (MODTRAN) atmospheric radiation model, the atmospheric radiation transmission theory is used to establish the limb infrared radiation model. Limb background infrared radiations are calculated at all latitudes in the typical wavelength ranges of 3~5 μm and 8~14 μm , including the seasons of winter and summer. The results show that the main factors affecting the limb background infrared radiation are tangent altitude, latitude, season, aerosol and wavelength range. These provide theoretical supports for the detection of limb background infrared radiation.