This paper explains the concept and characteristics of hidden toxicity in Chinese medical tumor,and discusses the biological connotation of hidden toxicity in lung cancer based on the occult tumor cells,such as circulating tumor cells,tumor stem cells,dormant tumor cells and so on. It is considered that the occult tumor cells are concealed and difficult to detect,they attack under the certain conditions,which similar to hidden toxicity in Chinese medicine. The discussion on modern biological basis of hidden toxicity could help to make clear the target of traditional Chinese medicine in the intervention on occurrence and metastasis of malignant tumor,and provide reference for precise treatment of traditional Chinese medicine. Meanwhile,it could further enrich Professor Liu Jiaxiang’s academic thoughts of strengthening vital qi to treat cancer,and also help to improve the clinical efficacy of traditional Chinese medicine.