Lung cancer is currently the malignancy with the highest incidence and mortality rate worldwide. In the past 20 years, due to the vigorous promotion of smoking cessation, the incidence of lung cancer in men in Western countries such as Europe and the United States has begun to decline, but the incidence of lung cancer in women has continued to rise. China is a major producer and seller of cigarettes, and the incidence of lung cancer has been on the rise in both men and women, especially in women. Clinical studies have shown that the cure rate of in situ cancer is close to 100%. It is suggested that early diagnosis is the key to improve the prognosis of lung cancer. However, due to the lack of ideal early diagnosis methods, the early diagnosis rate of lung cancer is only about 14%. Therefore, how to improve the early diagnosis of lung cancer has become a serious and urgent task for lung cancer prevention and treatment workers. Studies in areas with a high incidence of lung cancer have confirmed that it takes about 30 years from exposure to carcinogenic factors to the formation of clinical cancer (squamous cell carcinoma) [1]; the pattern of lung cancer incidence and mortality is consistent with the temporal pattern of smoking, with a latency period of more than 20 years [2]. This shows that lung cancer is a preventable and early diagnosed and treated disease, the question is how do we clinicians detect lung cancer during this long process? The clinical manifestations of lung cancer are complex and diverse. Most patients often have no obvious symptoms and signs in the early stage, and some patients may have cough, blood in sputum, chest and shoulder pain, fever, decreased appetite, and limited wheezing, but these manifestations are often ignored by patients or even professional physicians. Therefore, for early detection of lung cancer, firstly, it is necessary to vigorously strengthen the promotion of lung cancer scientific knowledge and advocate regular (every six months) screening for high-risk groups (men over 40 years old, heavy smokers, those with family history of tumor, those with history of occupational exposure and patients with chronic lung diseases, etc.). Secondly, respiratory physicians must have a strong sense of responsibility and solid theoretical knowledge, take medical history carefully, conduct comprehensive and careful physical examination, and maintain a high level of vigilance against lung cancer; they should pay close attention to the development of related disciplines and learn new knowledge in a timely manner. Only in this way can we fully grasp and scientifically apply the relevant examination methods, reduce missed diagnosis and misdiagnosis, and improve the early diagnosis of lung cancer. Imaging methods X-ray chest radiography is still the most common and basic method for lung cancer screening. A retrospective analysis of lung cancer cases found [3] that 90% of lung cancers had abnormal changes on early X-ray chest radiographs. The reasons for the missed diagnosis and misdiagnosis are: lesions hidden in hidden areas such as behind the heart, apical lung area, parapneumonic area, near the ribs and diaphragm; careless film reading; the presence of clear lesions and the omission of new lesions. In recent years, the application of computer-aided detection systems to display, identify, label and quantitatively analyze pulmonary nodules in digital chest images by contrast-enhanced viewing mode, node-enhanced viewing mode and automatic or manual segmentation modes has significantly improved the detection rate of lesions in overlapping and concealed areas.