CRISPR-Cas system is an acquired immune defense system that is found in some bacteria and most of the ancient bacteria. It makes the bacteria immune defense against the invasion of exogenous genes. In addition, CRISPR-Cas system plays a regulatory role in the formation of bacterial biofilm, drug resistance, virulence and other physiological functions, as well as in scientific research. According to this, we discussed the bacterial CRISPR-Cas system and its related research on the immune defense. Moreover, we described the regulatory function of this system in physiological function of bacterial and its future application, to provide a new idea for further study on bacterial resistance and pathogenicity.