With the limit of optical materials, it is difficult to design zoom optical systems which have long focal length by refractive systems with a simple configuration. All-reflective zoom optical systems could be lightweighted, compact and free of chromatic aberrations, and reflective optical systems can be unobscured by off-axis mirrors and have very good application foreground. In this paper, an all-reflective zoom optical system was designed, the all-reflective zoom optical system worked in the band of 400~1000nm, the diameter of the pupil was 100mm, the F number was 6~15, focal length varied from 600~1500mm, field of view (FOV) was 2°×0.8°~0.8°×0.48°. The pixel size of detector was 10×10μm. The result showed that MTF was higher than 0.3 at 50lp/mm and the quality of the optical system approached the diffraction limit, which met the design demand.