The sub-pixel measurement technique based on image processing technique and software design technique, is a good choice for the improving of measurement precision. The measuring technique and results of sub-pixel measurement accuracy of complementary metal oxide semiconductor (CMOS) imager are researched in this paper in order to give references for correlative systems. A test system based on high precision piezoelectric translator (PZT) fast-steening mirror (FSM) and OV7620 CMOS imager based digital camera is constructed, several sub-pixel measurement accuracy experiments for the CMOS imager are taken. The results indicate that sub-pixel measurement accuracy is about 0.17 pixel, it is of great importance to consider the influence of the fill-factor on sub-pixel measurement accuracy. According to the results above, CMOS imager has the capability to achieve sub-pixel measurement accuracy, and can be widely used in many measuring systems which count on facula centroid sub-pixel interpolation.