Inclusion Criteria:  ① Inclusion criteria for patients with COPD:  Over 18 years of age.  FEV1 / FVC< 70% was the diagnostic criterion for COPD after inhaling bronchodilators.  ② Inclusion criteria for high-risk subjects:  Over 18 years of age. Physical examination and routine laboratory tests were normal. Chest CT to exclude other pulmonary diseases. Lung function does not meet the diagnostic criteria for COPD. having one of the following risk factors: A. Smoking: current smokers, smoking index (number of years of smoking × number of cigarettes per day)≥ L.  B. Biofuel exposure: Subjects frequently use charcoal, wood, and animal dung for home heating and cooking Or crops are defined as having a history of exposure to biofuels. C. Dust and chemical exposure: mining, quarrying, casting, grain dust, paint, chemicals and others (including non-return) In the above categories of self-reported) occupational dust or gas smoke exposure for more than 1 year.  ③ Inclusion criteria of healthy control subjects:  Over 18 years of age. Physical examination and routine laboratory tests were normal. Chest CT to exclude other pulmonary diseases. Lung function does not meet the diagnostic criteria for COPD. No risk factors (including smoking, biofuel exposure, dust or chemical exposure).  Exclusion Criteria:  History of other chronic lung diseases, such as bronchiectasis, pulmonary interstitial fibrosis, etc. History of acute lung disease within 3 months. History of malignant tumor. Pregnant and lactating women.