A membrane diffractive athermal infrared optical system is designed. The optical system has an aperture of 200 mm, a focal length of 200 mm, a relative aperture of 1, a full field angle of 3., and a working wavelength of 10.7-10.9.m. The system uses the membrane diffractive lens as the primary lens, with the thickness of a micron, and has the advantages of large aperture and light weight, which solves the contradiction between the weight and the aperture of the existing infrared optical system. A hybrid refractive diffractive lens with a diffractive surface is used to correct the strong dispersion of the primary lens, effectively solving the problems of small field of view and narrow spectral range of the membrane diffractive primary lens. The use of membrane diffractive primary lens and refractive diffractive hybrid lens effectively utilizes the good athermalization characteristics of the diffractive surface. Combined with the selection of lens materials, it plays a good role in the athermalization of the optical system; the use of the diffractive surface increases the degree of freedom in the process of system design optimization. Membrane diffractive athermal infrared optical system has the advantages of light weight, good imaging quality, and excellent athermalization performance, which has a good application prospect in the field of infrared remote sensing imaging detection.