By reviewing the literature on the efficacy of tannins in traditional Chinese medicine in the last decade or so, we have classified the anti-tumor mechanism of tannins in conjunction with the latest mechanism exploration in the field of oncology. Tannins, a class of multi-phenolic compounds widely present in the diet, have been studied by scholars worldwide in recent years because of their relatively outstanding pharmacological activities. The mechanisms of anti-tumor action of tannins can be summarized as follows: the arrest of the cell cycle, arrest of tumor migration, enhancement of immune competence, induction of apoptosis, and antioxidant effects.