Abstract: To solve the problems of large volume and high development cost of high-resolution infrared cooled zoom imaging systems, a design method for a cooled infrared zoom optical system based on coaxial reflection was proposed. First, the imaging principle of the catadioptric zoom optical system based on a coaxial two-reflection configuration was analyzed, and a dual-focal-length optical system was developed by combining the coaxial two-reflection primary imaging group and the zoom secondary imaging group. The initial structure of the optical system was then calculated based on the design specifications and established initial structural equations, and a multi-recombination structure was established in the optical design software for the joint optimization of dual-focus aberrations. Finally, a dual-focal-length mid-wave infrared cooled optical system with focal lengths of -500 mm and -600 mm was completed. The F-numbers of the optical system were 2.5 and 3.0, respectively. The primary mirror aperture was less than 225 mm, the total optical length was less than 315 mm, the light-blocking coefficient was 0.32, and the modulation transfer function of the dual-focal-length optical system was close to the diffraction limit. This high-resolution infrared optical system can switch between different fields of view by simply moving the position of one zoom lens group, demonstrating broad application prospects in the field of all-day high-resolution imaging.