Flavonoids are natural products that are ubiquitous in the natural world, with wide physiological activities and low toxic and side effects. In recent years, their anti-tumor effect has caused widespread concern and studies. According to the findings, flavonoids have prominent effects in preventing and treating lung cancer, breast cancer, colon cancer, prostate cancer, liver cancer, leukemia, ovarian cancer, gastric cancer and so on. Their anti-tumor mechanisms mainly include anti-oxidation, anti-free radical, induction of apoptosis of cancer cells, impact on cell cycle, immune regulation, inhibition of tumor angiogenesis, inhibition of COX-2, inhibition of telomerase activity and so on. This article focuses on the advance in domestic and foreign studies on anti-cancer activity and mechanism of flavonoids, in order to provide theoretical basis and research ideas for the further development and clinical application of flavonoids.