Before the star sensor completes the attitude measurement task with the launch of the spacecraft, it must be calibrated on the ground. In order to meet the requirements of high precision star sensor calibration, according to the shortcomings of optical structure of conventional ground calibration equipment for large aperture, long focal length and wide spectrum requirements, an off-axis collimator was designed as a collimating optical system. The alignment method of the off-axis collimator was discussed, and the image quality was also evaluated. A set of lighting system is designed to precisely control the star point brightness. The LED array backlight is used as the light source, and the brightness of the light source is tested by an illumination meter. Experimental results show that seven consecutive magnitudes can be simulated, and the simulated error between neighboring magnitudes is less than 0.8%. The designed optical system can provide the ground calibration foundation for the development of deep space exploration star sensor.