The development of third-generation infrared focal plane detectors allows them to respond simultaneously to two different bands of infrared radiation, and the dual-band image brings significant benefits to target detection and identification. In this paper, a cooled infrared dual-band zoom optical system with large-magnification-ratio is designed for aerial detection applications. The system includes a 320×256 dual-color infrared-cooled detector. It operates in the bands of 3.7-4.8 μm in mid-wave and 7.7-9.5 μm in long-wave. The optical system adopts the combination of refractive and catadioptric structures to realize an optical four-field-of-view switching wide-range zoom. In order to realize the 100% cold diaphragm efficiency, a secondary imaging mode is adopted. The four-field-of-view focal lengths of the optical system are 32 mm, 200 mm, 800 mm, and 1600 mm, and the zoom ratio is 50×. The experimental results show that the optical system is close to the diffraction limit at a modulation transfer function eigenfrequency of 17 lp/mm in each dual-band zoom state. The optical system has dual-band characteristics, extensive zoom ratio and large range, fast switching of multiple fields of view, simple and compact structure, and high-quality imaging, which will be useful in a wide range of security fields such as searching, reconnaissance, and so on.