Abstract:The discovery of CRISPR-Cas system breaks certain theory which adaptive immunity had been long time considered as unique characteristics of eukaryotic organism. CRISPR-Cas, a new adaptive immunity system widespread in bacteria and archaea, protects the host from invasion of exogenous nucleic acids by capturing and using the Cas protein and crRNA to resisting it when invading again. In recent years, CRISPR-Cas system has aroused extensive attention and exploration. From microbial perspective, this article introduces a brief overview on classification, mechanism and application which have achieved significant breakthrough to provide valuable reference for further research on CRISPR-Cas system and its application.