According to IR radiation′s principle,the calculating method of airplane′s IR radiation on the basis of temperature field distributing is proposed.The useful object information which the IR detector receives after atmosphere′s transmission is gained.By calculating and analyzing the detected distance of a certain plane,five significant characteristics of airplane′s infrared radiation that influence the detecting effect are pointed out,which include spectrum characteristic,direction characteristic,altitude characteristic,velocity characteristic and engine state characteristic.Based on the conclusions,problems about IR detector and plane′s IR stealth are discussed.