Abstract: An optical simulator was designed in loop testing of medium and long range angles-only navigation of spacecraft, which can verify the performance and reliability of the hardware, software and algorithms of the angles-only navigation vision sensor. Firstly, the system description of the optical simulator was given, including the hardware composition and the star map simulation software design. The commercial and off-the-shelf components were selected as the hardware, which could greatly save research and development costs and shorten the development cycle. Then, the relationship between screen brightness and star magnitude, and the optical principle of the optical simulator were emphatically introduced. Finally, the star map simulation of the optical simulator was tested, and an angles-only navigation model based on Clohessy-Wiltshire (CW) equation was introduced for hardware in loop testing, which verified the optical simulator after geometric calibration could be used for hardware in loop testing of medium and long range angles-only navigation of spacecraft. The relative position accuracy is increased by 25.5%, and the relative speed accuracy is increased by 31.3% compared with that before geometric calibration at the terminal time.