To realize the low-cost and athermalization design of medium-wave infrared seekers, a high-resolution medium-wave infrared imaging guidance optical system with infrared imaging guidance was designed with low-cost and wide-temperature-range athermalization. The general layout is a two-axis frame; the system chooses one imaging configuration with three pieces of lenses based on Si/Ge material. The detector chooses a Stirling-cooled 640 pixel×512 pixel detector with the pixel size of 15.m. The prototype design results show that the optical system focal length is 100 mm, field size is 10°×8° at 33 lp/mm, the axis view of the modulation transfer function (MTF) is not less than 0.6, 0.7 field of the off-axis modulation transfer function (MTF) is not less than 0.40, the system distortion is less than 1%, and the efficiency of the cold stop is 100%. Moreover, the narcissus of the system is almost elimination based on pertinence optimization design with fairing. In the temperature range of -40 to 70℃, good image effect was realized. The optical system has the advantages of a simple structure, ease of processing and adjustment, and high yield rate; the imaging quality of the optical system is excellent, and the performance indexes meet the technical specifications.