Modern medicine refers to precancerous diseases that may turn into cancer but not necessarily into cancer, while precancerous lesions are a pathological concept that refers to some pathological conditions that may turn into cancer. Pre-cancerous diseases are often combined with pre-cancerous lesions. According to the standard of World Health Organization, only those lesions with a risk of malignant lesions greater than 20% are classified as precancerous lesions. The idea of “treating the disease before it occurs” in the Yellow Emperor’s Classic of Internal Medicine guides the prevention of oncology in Chinese medicine. (1) Preventing diseases before they occur. Physical exercise or food and drug conditioning according to physical condition, adapting to external environmental changes, changing living habits: quit smoking and alcohol, avoid eating moldy and unclean food, adjusting the mentality, etc. (2) Prevention of both diseases and changes. Focus on the treatment of nasopharyngeal mucosal hyperplasia, benign thyroid tumors, esophageal mucosal hyperplasia, gastric ulcer, atrophic gastritis, residual gastric lesions, multiple gastrointestinal polyps, viral hepatitis, liver cirrhosis, benign breast tumors, cervical erosion, gravida, benign ovarian tumors, skin keratosis, hyperpigmentation, scarring, mucosal white spots, residual lung lesions and other precancerous lesions, and inhibit and control their further cancerous changes. (3) Already changed to prevent progression. To stop and slow down the development of tumor. Modern tumor prevention has changed from “early detection, early diagnosis and early treatment” to “less occurrence and easier treatment”. The prevention and treatment of precancerous lesions in Chinese medicine has achieved obvious results.