On the basis of the dual-band athermal theory, a cooled dual-band infrared refractive-diffractive hybrid optical system of athermalized and wide field of view was designed. The system consists of 4 lenses and introduces only 1 diffractive surface and 1 aspherical surface, the full field of view is 80.2°, the focal length is 8 mm, F number is 2, the operating wavelength range is 3.5~4.8μｍ and 8~12μｍ, and the cold stop efficiency is 100%. The solutions of 4 separate thin lenses were obtained by analyzing dual-band achromatic and athermalized theory. Further, establishing the material model of athermalized dual-band optic system and choosing the optical materials properly. According to requirements, the dual-band athermal optical system with temperature of －40℃ to 60℃ was designed with the use of optical passive. The reasults prove that the optical system obtains a good image quality during －40℃ to 60℃, and realizes athermalization.