1. Patients who meet the diagnostic criteria for COPD of the global initiative for chronic obstructive lung diseases (GOLD 2022) and GOLD grading Ⅲ - Ⅳ (FEV1/FVC\<70%, FEV1% predicted value ≤ 50% after Bronchiectasis)
2. Age\>40 years old
3. COPD stable for more than 4 weeks
4. Short acting Bronchiectasis was not used within 24 hours before this experiment, long acting Bronchiectasis was not used within 48 hours, and glucocorticoids were not used throughout the body in the past month
5. Patient informed and signed consent form
You may not be if
1. Asthma, active pulmonary tuberculosis, interstitial pneumonia and severe Bronchiectasis
2. Complicated with serious diseases (acute infection, diabetes, stroke, heart disease, liver and kidney dysfunction, cancer or autoimmune disease)
3. History of chronic diarrhea or constipation
4. History of Gastrointestinal Surgery
5. Using probiotics or antibiotics within the past 4 weeks
6. No history of using oral hormones or traditional Chinese medicine in the past three months
