In addition to the advantages of traditional infrared intensity imaging, such as long detection distance, all-weather working and good concealment, infrared polarization imaging technology based on the difference between the target and background polarization characteristics can effectively reduce background interference, suppress background clutter, enhance image contrast, improve signal-to-noise ratio, and has broad application prospects. In order to effectively suppress the background clutter interference in the process of air and sea detection, enhance the target detection ability in fog, haze and smoke, as well as the backgrounds of small temperature differences and low illumination, the design of a four channel aperture sharing medium-wave infrared polarization imaging optical system with a focal length of 240 mm was completed. Tolerance analysis was carried out by using Monte Carlo method to ensure the rationality of the precision of optical system processing and assembly. The results of image quality analysis show that the MTF of the optical system is close to the diffraction limit, aberrations have been effectively corrected, and the imaging quality is good. The influence of Narcissus effect on the imaging quality of the cooled infrared optical system was verified by Narcissus analysis. In addition, the optical system proposed has a compact structure and high transmittance, avoiding the use of aspheric surfaces, and has good processing and assembly technique.