The clustered regularly interspaced short palindromic repeats (CRISPR and CRISPR-associated system,CRISPR-Cas system) is an acquired immune system found in most bacteria and archaea,consisting of Cas enzyme and guide RNA (guide RNA,gRNA),which recognizes and shears target DNA or RNA based on the specificity of gRNA sequence. In recent years,thanks to the excellent enzymatic activity of the CRISPR-Cas system,a variety of biosensing technologies (biosensor) have been established,and optical signal sensing strategies are simple,portable,and widely used in scientific research and practical applications. We summarized in detail the basic principles and representative results and applications of various optical sensing strategies based on the CRISPR-Cas system in the last five years. Also,we provide an outlook on the current application prospects and challenges.