As the substitute material of optical crystal, the characteristics of chalcogenide glass with high spectral transmittance, high thermostability, moldable property and low price received extensive attention. An infrared athermalization optical system was designed based on temperature characteristics of chalcogenide glass and theory of optical passive athermalization. The working band was from 8 μm to 12 μm, the F-number was 1, the field angle was 38°, and the overall length was 16.7 mm. The system was composed of three lenses, which used two chalcogenide glasses materials, IRG202 and IRG206 respectively, only introduced two even aspheric surfaces, and no diffraction surface was used. The system had advantages of compact structure, low cost, and high luminous flux, which was compatible with uncooled infrared area-array detector that had pixel elements of 384×288, and pixel size of 17 μm. From -40 ℃ to 60 ℃, the MTF of designed lens of each field of view is greater than 0.4 at the nyquist frequency, and the imaging performance of optical system is stable. The system can be widely used in the field of vehicle night vision and security monitoring.