An optical system of mid-wavelength infrared for high resolution cooled wide-angle imaging system is designed. The F-number of the system is 2 and full field of view (FOV) 2ω=111.2°. The system chooses a double imaging configuration. By introducing an diffractive optical element, setting aspheric surfaces and symmetrically distributing three types of material Si, Ge and ZnSe with 6 elements, the system is athermalized across a wide temperature range from -55 ℃ to +80 ℃ and the optical aberration is well balanced. In the athermalized temperature range, the modulation-transfer function (MTF) is higher than 0.4 at 33 lp/mm, and the diffractive radial energy is more than 70% in a circle of 15 μm. Based on the principle of f-θ lens, the wide-angle system gets the same angular resolution for different fields. By intently introducing stop aberration and specifically controlling the FOV in imaging space, the focal plane gets a very good illumination uniformity, the relative illumination of off-axis field is more 90.9% and the efficiency of the cold stop is almost 100%. Moreover, the narcissus of the system is controlled very well. This system is suitable for high resolution cold 640 pixel×512 pixel detector with pixel size of 15 μm.