Inclusion Criteria:  ≥10 pack-years smoking history; Examination of pulmonary function and compatible computed tomography meeting group requirements (as shown in Groups and Interventions).  Exclusion Criteria:  Take antibiotics, probiotics, prebiotics, synbiotics and other drugs that obviously interfere with intestinal microbiome within 2 months; Suffer from other chronic respiratory diseases other than COPD (such as bronchial asthma, allergic rhinitis, pulmonary interstitial fibrosis, bronchiectasis, lung cancer, etc.); Suffer from severe intestinal diseases (such as inflammatory bowel disease, intestinal infections, colorectal cancer, etc.); Suffer from serious hematopoietic system diseases, and the brain, heart, liver, kidney and other important organs are damaged; Suffer from severe hypertension, coronary heart disease, diabetes and other chronic diseases and taking drugs for long-term maintenance; Suffer from active infectious diseases (hepatitis B, tuberculosis, etc.); Pregnant or lactating women; Patients with obvious anxiety, depression and other psychiatric symptoms and patients with schizophrenia.