Usually, atmospheric visibility is used to describing the atmosphere′s visual effects in the visible light, but it does not apply to infrared wavelengths. In view of the visualized characteristics of atmospheric visibility and the pressing needs of the infrared electric technology, based on the infrared system contrast threshold, referring to the definition of visible light atmospheric visibility, the concept of infrared atmospheric visibility is put forward. According to the definition presented here and the physical process of infrared atmospheric transmittance involved in, the key determinants factors of infrared atmospheric visibility are analyzed. Generally, these factors are atmospheric visibility of visible light, absolute humidity and aerosol types. the quantitative relationship between the infrared atmospheric visibility and these factors is estabished, and the infrared atmospheric visibility of atmospheric windows (1.06,3~5,8~12μm)is calculated, whose noise equivalent temperature difference (NETD) is 0.05 K.