Abstract: Based on the operation requirements of an vehicle-borne observation and sighting simulation system and Gaussian optics theory, a three-group telescope zoom eyepiece was designed with Zemax. In order to obtain better image quality and long exit pupil relief, a three-group structure was adopted, and the pupil position was set as an optimized variable to make the entrance pupil position unchanged for continuous zoom. The focal length is f=（13.35～24.11） mm, exit pupil relief is L=（20.1~27.5）mm, exit pupil diameter is about 8 mm, image plane range is y=（3.9～14.06）mm, and zoom ratio of telescope zoom eyepiece is1.83. At 50lp/mm, the MTFs of four configurations are greater than 0.3, the spot diagrams of all configurations are smaller than Airy disk radius and higher than human eye resolution limit, which meet user requirements. Finally, the curves are fitted by Matlab, the corresponding focal length curves are given, and the fitting accuracy reaches 0.01mm.