Abstract: ［Abstract］Recently，a fast developing new technology for gene modification named as CRISPR-Cas9 which based on CRISPR-Cas9 system composed of clustered regulatory interspaced short palindromic repeat（CRISPR） and Cas9 nuclease（CRISPR associated system 9，Cas9）has been developed. CRISPR-Cas9 system is a kind of immune mechanism widely found in bacteria and archaea. This mechanism can help bacteria and archaea against exogenous DNA by the approach of specifically breaking DNA. Later，this mechanism was found to be useful for gene modification and gene deletion. At present， this technology has been applied to gene modification and therapy. Many studies have shown that the technology，compared with other genetic technology，has higher efficiency and accuracy，and it has promoted genetic engineering progress. Summarized here is the principle and application advance of CRISPR-Cas9.