Abstract: Star maps are the indispensable and important data in the research on star sensors. It is a short cut to perform star map simulation utilizing computers. A method was presented to simulate the procedure of optical system imaging for star sensors to obtain star maps by extension programming. A system to simulate star maps was established. Firstly, the necessity of extension programming to realize imaging simulation by taking advantage of the extension interference was discussed on the basis of analyzing the basic principle of simulating optical system imaging for star sensors. Then, the methods to simulate imaging, add false stars and noises to maps, store and output star maps were introduced. Complete applications of extension programming were also introduced. Finally, the design result of the system to simulate star maps was given out. Examples were also presented as for the given optical system. The simulation method was validated. It is proved that the simulation method is correct, and can be handled easily and simply. Programming workload is less. The simulation system has advantages of fine interface, versatile, and has the ability to offer rich and multiplex data. It is significant to promote the study of star sensor technologies.