To meet the requirements of a photoelectric imaging system with low cost, wide operating temperature range, compact size, light weight, and low power consumption (SWaP), a catadioptric optical system with secondary imaging was designed using a half-structure design method. The front and rear groups were designed separately, with thermal dispersion and aberrations offset. The front group consists of a spherical primary mirror, a high-order aspheric secondary mirror, and a spherical lens in front of the primary image plane, while the rear group is a four-piece relay lens assembly. This system uses a 640×512 focal plane arrays with an F#3 medium-wave infrared refrigeration detector. The wavelength range is 3.7–4.8 μm; the focal length is 200 mm; the obscuration ratio is no more than 1/3.33; the field of view (FOV) is 2.2°× 2.75°; the cold stop is 100% matched; the total length is less than 120 mm; the operating temperature range is –45℃ to 60℃. Across the full temperature range, the modulation transfer function (MTF) at the central FOV is ≥0.4@33 lp/mm, and at the edge FOV is ≥0.32@33 lp/mm. The equivalent temperature difference of Narcissus is ≤0.45℃ at an ambient temperature of 20℃.