Abstract: In order to realize the on-line detection of the surface defects of optical elements in the telescope system, a zoom imaging optical system for the detection of the surface defects of optical elements was introduced. Firstly, some key parameters of the zoom system were calculated according to the technical requirements of the telescope system. Then, the final result was obtained after design and optimization with Zemax software. Thewhole zoom system achieves a 6-fold continuous zoom with a focal length of 90 mm~540 mm. During the zoom process, the F number and image surface position of the system remain unchanged, and the design results show that the total length of the zoom system is 553.1mm.Finally, we analyzed the imaging quality of the system from modulation transfer function (MTF) and point sequence diagram.The MTF value of the system at each focal length is greater than 0.3 in 100 lp/mm, and the object resolution is better than 0.055 mm. The root mean square value of the diffusion spot radius of the system at different focal lengths is controlled within the airy spot radius. In addition, we also analyzed the environmental adaptability of the system, studiedthe imaging quality of the system in the temperature range of -10℃~40℃, and gave the temperature compensation scheme. The imaging quality of the whole system is good and can meet the actual demandafter compensation.