Abstract: In order to change the focal length of optical zoom system without using moving parts, two or more active optics were added, which could provide variable focal length and create an imaging system with variable magnification. Based on this design concept and combined with Cassegrain reflective telescope, a zoom system was designed with active optical elements in ZEMAX. Its effective focal length is from 1600mm to 800mm, and its field of view (FOV) is 0.6～1.2. The whole system consists of 2 reflective deformable mirrors, 1 fold mirror and 1 refractive lens. In order to achieve zoom function, the entrance pupil diameter, the first and the second reflective mirrors radius are variable. Its MTF at the spatial frequency of 16lp/mm is more than 0.75, the maximum RMS spot diameter is less than detector size. The results show that the imaging quality can satisfy system requirements.