To achieve the high-resolution detection of space infrared telescopes, based on the Schupmann ach-romatic theory, the design and athermalization model of catadioptric middle infrared diffractive telescope system with large aperture were studied. An optical system which had an aperture of 1 m, F-number of 2, full field of view of 0.12°, waveband of 3.8 μm~4.2 μm was designed, the primary mirror and correction mirror were plane diffractive lenses, the relay system adopted catadioptric Cassegrain structure, and the refocusing and three times imaging systems used refractive structure, then the tolerance, ghost image and cold reflection of the system were analyzed. The design results show that at the temperature of -20℃~60℃, the MTF of the system is greater than 0.7 in the range of 16.7 lp/mm, close to the diffraction limit, and has 100% cold shield efficiency. The tolerance of system satisfies requirements of fabrication, the ghost image energy is 0.1%, which has little influence on the target signal, and the Narcissus induced equivalent temperature difference (NITD) value of cold reflection with temperature is less than noise equivalent temperature difference (NETD). The system can provide reference for the design of larger aperture infrared diffractive telescope system.