Abstract: Based on mid-wave infrared (MWIR) (320240) cooled detector, an infrared miniaturization and continuous zoom optical system adopting mechanical compensation method, employing diffractive optical element and folded beam path was designed. Using zoom system principle and Zemax optical design software, the optical design parameters were offered, image quality evaluation was presented and cam curve was solved. The design results show that six lenses are used in system, continuous zoom of 18 mm ~ 360 mm is achieved at band of 3.7 m~4.8 m, and cold optical stop matching is 100%. The value of modulation transfer function is all above 0.5 at the spatial frequency of 16 lp/mm. The system is characterized by large zoom ratio, excellent images, miniaturization and smooth zoom locus. It can be used for airborne electro-optical detection equipments.