As we all know, once the symptoms of lung cancer are detected, most of the patients are in the advanced stage of lung cancer, so how can lung cancer be detected early? What manifestations should cause high alert? For smokers who have the following clinical characteristics, especially those over 40 years old, they should immediately take corresponding examinations for early diagnosis and differential diagnosis: ① irritating cough without obvious causes lasting 2-3 weeks, and treatment is ineffective; ② original chronic respiratory diseases and recent change in the nature of cough; ③ persistent or repeated blood in sputum or hemoptysis within a short period of time, and no other causes can be explained; ④ repeated episodes of pneumonia in the same area, especially lung segmental pneumonia; ⑤ pneumonia of unknown origin (5) Unexplained lung abscess without history of foreign body inhalation and toxic symptoms, without large amounts of pus sputum, and with poor anti-inflammatory treatment; (6) Unexplained joint pain in the extremities and pestle-like fingers (toes); (7) Imaging suggests limited emphysema or segmental or lobar atelectasis, with suspected stenosis of the connecting bronchi; (8) Isolated round or round-like lesions and unilateral hilar shadow thickening and enlargement; (9) New lesions in other parts of the lung with a stable original tuberculosis lesion (9) new lesions with changed morphology or nature, lesions that increase in size or form cavities after anti-tuberculosis treatment, and sputum negative for tuberculosis; (10) pleural effusion without toxic symptoms, especially if it is bloody and progressively increasing. The presence of one of the above manifestations warrants suspicion and requires necessary ancillary examinations, including imaging, especially low-dose CT scan, which is currently a valuable method for census detection of lung cancer.