A long-wave infrared optical system to detect the refrigeration type CCD for airborne despun device was designed.The re-imaging configuration was used to meet cold shield efficiency requirement，and optical passive athermalization principle was applied to achieve athermalization compensation with a wide range of temperature.The aberrations are corrected by the aspherical-diffraction element，and the effect of diffraction element shape error on the optical system is discussed.The design results show that this system has compact structure and light weight.It realizes the athermalization compensation in the temperature range of -40~60℃.100% cold aperture efficiency and the controlling cold reflection are also achieved.