Abstract: Star simulator，as the ground calibration system of star sensor, can be used to simulate the star involving its size, magnitude，spectrum，color temperature，position and the angular distance between stars，etc.With the continuous development of space technology，the requirement of the star simulator itself has become higher, and then the design of collimation optical system for star simulator important component has become the key factor. Based on the characteristics of off-axis reflective optical system which has no chromatic aberration，small volume，high light efficiency and the center without blocking， an off-axis parabolic collimation optical system was proposed,and the assembly and calibration process was discussed. The system consists of an off-axis parabolic mirror and a plane mirror，which has a clear aperture of 300 mm，focal length of 3 000 mm，and viewing angle of 30.The image quality analysis shows when the distortion in field of view is 0.006 2%（0.01%), the modulation transfer function (MTF)reaches the diffraction limit and the wave aberration is 0.071 6 .This design of the optical system can meet the requirements.