In the practical application of star sensors, the presence of stray light in the optical system will cause the star points to be blurred or blocked. Based on the requirements of the star sensor for aperture, field of view, spectral range and detection capability, the optical system design of star sensor was completed using Code V software. The final design parameters were 15 mm diameter, 18 degrees field of view, spectral range from 400 nm to 750 nm, detection capability 5 grade stars. A cone structure hood was designed with CAD drawing software, shading field of view boundary of the hood blade was 19°, and there were 9 light blocking rings in total. The front end face was 190.76 mm from the window glass, the front end face diameter was 108.76 mm, and the sun avoidance angle was 25°. At the same time, the ASAP software was used to analyze the optical system's ability to suppress stray light. According to the stray light evaluation index point source transmittance(PST), the system satisfies the detection capability requirements of 5th magnitude stars at a solar avoidance angle of 25°, which verifies the stray light analysis the correctness of methods and analytical models.