As the name implies, precancerous lesions are abnormal changes that occur before the appearance of cancer and are not cancer. Pre-cancerous lesions in lung adenocarcinoma usually appear as “gross glassy changes”, which is a morphological description of pre-cancerous lesions in lung adenocarcinoma on CT scans, which look like gross glass and are translucent. It appears as an atypical adenomatous hyperplasia on pathological sections. Precancerous lesions of lung squamous carcinoma are usually located on the surface of the bronchial lining and are not easily detected by normal bronchoscopy and can only be seen by fluoroscopic bronchoscopy. Histologically, squamous precancerous lesions are called squamous epithelial atypical hyperplasia. There is debate about the management of precancerous lesions. Simple intrapulmonary GGO should be closely followed and once it increases in size or becomes solid in texture, it should be aggressively surgically removed because such changes are likely to indicate that the precancerous lesion has transformed into lung cancer. Precancerous lesions of squamous carcinoma are actually rarely detected clinically, because such lesions do not show abnormalities in CT or routine bronchoscopy first. Most of them are detected during screening of high-ranking people, such as heavy smokers and previous history of squamous lung cancer.