Based on the previous work of LDCT screening, in order to improve the screening rate of central lung cancer for LDCT negative and severe smokers, the investigators plan to conduct China's first large-scale fluorescent bronchoscopy screening test.

CT scan is a commonly used method for clinical screening for early lung cancer, but research shows that LDCT scan has a higher detection rate for peripheral lesions (often adenocarcinoma), and a lower detection rate for central lung cancer (mostly squamous cell carcinoma). Fluorescent bronchoscopy uses the principle of differentiating fluorescence in different tissues to distinguish normal parts from diseased parts. It is often used for screening of central early lung cancer.Based on the results of the investigator's previous research, the investigators plan to conduct a second round of community screening-bronchoscopy screening, and perform white light bronchoscopy and autofluorescence bronchoscopy screening for high-risk groups of lung cancer with heavy smoking (≥400 years) and no obvious lung nodules.

Inclusion Criteria:

1. Age 45-75 years;
2. have a smoking history of ≥20 pack years; if participants quit smoking, it should be <15 years;
3. Chest LDCT examination within one and a half years without obvious abnormalities or calcified nodules or non-calcified nodules and no signs of malignancy

Exclusion Criteria:

1. Non-smokers or mild smokers;
2. There are contraindications to bronchoscopy, such as active hemoptysis, unstable angina pectoris, coagulation dysfunction, anesthesia allergy, etc .;
3. Refusing to sign informed consent;
4. The operator believes that the patient has other conditions that are not suitable for bronchoscopy.