To correct and balance aberrations found in current systems, we designed a catadioptric telescope objective with a large relative aperture, long focal length, and short total length by adding a set of refraction optical elements before and after a double-mirror system. The working band of the objective system is 400-700 nm, focal length is 900 mm, diameter of the entrance pupil is 500 mm, obstruction ratio is 0.43, total length of the system is 495 mm, and value of modulation transfer function in the full field-of-view range is more than 0.5 at a cut-off frequency of 107.5 lp/mm. Tolerance analysis of the system was conducted. The results show that the telescope objective system designed in this study has the characteristics of a simple structure, high imaging resolution, and large tolerance.