Theabrownin, a kind of water-soluble, non-dialysable, highly polymerised brown substance, mainly composed of polyphenol, polysaccharide, protein and nucleic acid, which is closely related to the color and functional activity of fermented tea. Due to the complexity of the formation mechanism, its chemical structure is still unclear. In this review, the structural characteristics, formation mechanism, extraction and detection methods, and functional activity of theophylcin were discussed, and the future research direction was also prospected.