In order to improve the operational efficiency of medium and long-range precision strike equipment in complex battlefield environment, and to realize medium/long-wave, common aperture, high resolution and athermalization in photoelectric detection system, a high resolution athermal infrared optical system with composite common aperture of medium/long-wave is designed. The system selects the strapdown general structure design with high maturity and stability. Based on medium/long-wave combined cooling infrared 640×512 pixel detector with pixel size of 24 μm, the system uses one imaging with four-piece optical structure, and introduces a binary diffraction plane. The parameters of the optical system are as follows: the system focal length is 19 mm, field size is 44°×35°, the optical distortion is less than 2%, the cold diaphragm efficiency is 100%, and the modulation transfer function curve is straight. The light collecting ability is strong, the structure is simple, and the reliability is high. In the working environment within the temperature range of -40~+70℃, the cooling infrared system has excellent imaging quality and strong environmental adaptability in the medium/long-wave band, and satisfies the usage requirements.