Flavonoids are widely distributed in the nature, and have various biological activities. Flavonoids can be degraded by intestinal bacteria, so as to impact their bioavailability in vivo. Studies on metabolism of flavonoids by intestinal bacteria could provide basis for screening out biotransformation of flavonoids and interpreting their in vivo metabolic process. Being taken as the lead compounds, flavonoids can be modified by intestinal bacteria to achieve new compounds with high efficiency, bioavailability and solubility, which lays a foundation for the research and development of new drugs, selection of drug dosage forms and drug production. This article summarizes the main reaction types and impacting factors of intestinal bacteria on biotransformation of flavonoids, for reference of studies on biotransformation.