Polyphenols are important secondary metabolites in plants, which have health benefits such as antioxidant, antiinflammatory and anticancer effects. However, most polyphenols have low bioavailability after entering the gut. Studies have shown that microbial transformation can improve the availability of plant-based foods. In this article, the biotransformation of different phenols by microorganisms during the fermentation of plant-based foods is reviewed, and the changes in the composition and bioactivities of polyphenols before and after fermentation are analyzed, which is of great significance for revealing the mechanism of microbial transformation of polyphenols and for optimizing the application and development of polyphenols.