The treatment effect of lung cancer depends on the early and clear diagnosis of lung cancer, but the early diagnosis of lung cancer is difficult, so people with high-risk factors or suspicious signs should have regular examinations related to cancer prevention or exclusion, especially for people over 40 years old and long-term heavy smokers who have one of the following conditions: 1. 2. chronic respiratory diseases, such as chronic bronchitis or chronic obstructive pulmonary disease, with a change in the nature of the cough such as aggravation of the cough, change of intermittent cough to persistent cough, or high-pitched metallic sound; 3. persistent or repeated blood in the sputum or hemoptysis within a short period of time without other explanations; 4. recurrent episodes of pneumonia in the same area, especially those confined to one lobe; 5. Pulmonary septic infection of unknown origin, without toxic symptoms such as chills, high fever, malaise, general malaise, loss of appetite, no large amount of pus sputum, no inhalation of foreign bodies, and no significant effect after anti-inflammatory treatment; 6, joint pain in the extremities of unknown origin and pestle-like fingers (toes) (hyperplasia, hypertrophy, pestle-like expansion of the ends of the fingers or toes); 7, limited emphysema on X-ray, or a pulmonary segment or a 8. isolated round lesions and unilateral enlarged hilar shadows are seen on X-ray; 9. the original tuberculosis lesions have been stabilized, but there is a change in morphology, burr or cut marks on the edge of the lesions or a change in the nature of the lesions; 10. pleural effusion is present, but there is no fever, malaise and other toxic symptoms, especially if the effusion is bloody, large and rapidly increasing. It is worthy of suspicion, and necessary auxiliary examinations, including sputum exfoliated cells, bronchoscopy and imaging examination, especially low-dose CT scan is a valuable method to detect lung cancer by census at present.