By analyzing the influence of the optical system structural parameters on aberrations, a method was proposed to reduce the primary aberrations of each optical surface by optimizing the curvature to make a reasonable power distribution, which could reduce the processing and adjustment tolerance sensitivities. Using this method, a nano-star sensor optical system with a focal length of 25 mm, a full field of view of 26°, entrance pupil diameter of 18 mm and spectrum range of 500~800 nm was designed, which was a small aberration compensation system. The whole length of the system was 40 mm. The imaging quality of the optical system met the requirements. Tolerance sensitivity analysis was carried out for two optical systems. The results show that the influence of the thickness tolerance of the fifth lens on the Root Mean Square (RMS) spot radius decreases from 3.75 μm to 0.17 μm in the reasonable power distribution optical system; and the influence of the fifth and sixth element spacing tolerances on the RMS spot radius decreases from 4.36 μm and 4.74 μm to 0.25 μm and 0.18 μm, respectively. Monte Carlo analysis shows that the probability of the RMS spot radius of less than 7.59 μm is increased from 23% to 80%. The experimental results show that in the full field of view the energy concentration of the star sensor is better than 80% in the range of Φ17 μm, which meets the requirements.