Detecting a 4.5 magnitude star in the observation height of 10 km, the radiance of stars between 600~1 100 nm was analyzed, the radiance of sky background and the optical transmission of atmosphere were calculated by using Modtran. When the threshold of SNR is 5, typical parameters are selected. With a plane mirror and a silicon material sphere lens, a lighter miniature optical system was designed. The result shows that the optical system spot shape approaches a circle between 600~1 100 nm of full field of view, modulation transfer function approaches perfection and have outstanding image of quality. The Ground-based daytime and nighttime detection SNR of the star tracter is calculated and the detection ability limit is estimated in the threshold 5 of SNR, which is 2.5 stellar magnitude G star in daytime on the ground and 6 at night.