In order to improve the ability of the star sensor to detect limited magnitude, a combination of the improved Cassegrain system, aperture-corrected spherical lens group and field-of-view corrected spherical lens group is adopted to design an optical system of a large aperture catadioptric star sensor capable of correcting astigmatism, field curvature and distortion, with the spectral range of 450~950 nm, the semifield of 1.4°, an entrance pupil diameter of 250 mm and the focal length of 425 mm. According to the calculation of the initial structure parameters of the system based on the aberration theory and the optimization design of Ray tracing in Zemax software, the blocking ratio of the secondary mirror of the optical system reaches 0.43, the energy concentration of the imaging point is 80% within 30 μm, and the maximum distortion is 0.081%. The modulation transfer function is greater than 0.75 at a Nyquist frequency of 34 lp/mm, and the maximum magnification chromatic aberration is 1.138 μm, which meets the imaging requirements of star sensor pairs. Through the tolerance analysis of optical system, in the 20 Monte Carlo analysis results, the best structure is the 13th structure with the performance function of 4.975 16 μm, the worst structure is the 20th structure with the performance function of 7.799 57 μm. Through the performance function analysis of 20 times Monte Carlo structure, the selected tolerance value can well meet the basic requirements of optical system performance, and provide the basis for the errors in the process of processing and installation.