Abstract:Microsatellite instability（MSI）refers to the phenomenon of the length or structure changes of microsatellite regions due to defects in the function of the DNA mismatch repair system，which is usually closely related to the development，progression，prognosis and treatment of tumors. Therefore，the detection of MSI is of great significance for tumor treatment. At present，MSI detection methods mainly include polymerase chain reaction，immunohistochemistry and next-generation sequencing. By detecting changes in microsatellite loci or the expression of DNA mismatch repair system proteins，the status of MSI can be determined，so as to guide tumor treatment. This article describes the mechanism and detection methods of MSI and the clinical significance of MSI detection.