A zoom lens is designed for a specific airborne platform. In order to decrease the axial dimensions, the rear-view mirror group is folded twice. It meets the space requirements since the axial dimension of the optical system is 96 mm. The zoom ratio of lens is 20, and the focal length is 6~120 mm, and the relative aperture is 1/5.6. The lens uses a method of mechanical compensation and a guiding mechanism of carriage. The lens has a small axial size, with high accuracy and a small optical axis shaking. Through the test, the optical axis shaking is found to be no more than 34″ in the process of continuous zoom. Through flight test, it is proved that the zoom lens can search objectives in the short focal length and track the target in the long focal length. In addition, the zoom lens can quickly change the focal length, the obtained image is stable, and the tracking video image is clear.