The star sensor is composed of an optical system and a photoelectric sensor, and the former is the most important part. The star sensor optical system requires high imaging quality and good technical indexes, and its volume and weight are strictly limited, so that the corresponding optical design is difficult. In the premise of meeting volume requirements, the best system structure is selected, and the focal power is reasonably distributed to reduce distortion and high order aberration. At the same time, the system is made as a telecentric light path. Special dispersion glass is adopted to correct chromatic aberration of wide band range, and the asphere is adopted to improve imaging quality. The results show that the measured modulation transfer function (MTF) of each field is more than 0.344 (at Nquist frequency), the laboratory static MTF is more than 0.2 (at Nquist frequency), 80% of the imaging dispersion spot energy is focused inside 23 μm, and the relative distortion is less than 0.1%. The technical indexes and the imaging quality requirements are satisfied.