Inclusion Criteria:  Male or female, aged 18 ~ 75 years. Patients who meet the diagnostic criteria of Rome IV of Irritable Bowel Syndrome and are definitely diagnosed as IBS-D. IBS has been diagnosed for more than 6 months, and has been treated with conventional drugs without obvious curative effect or repeated attacks. No other serious diseases, no mental disorders, and normal communication skills. Sign informed consent and agree to participate in this study. No antibiotics and probiotics were used within one month.  Exclusion Criteria:  Patients are unwilling to participate in this study. Other serious diseases of heart, liver, kidney, respiration, digestion, blood and endocrine system. Combined with intestinal double infection, such as CDI, enterohemorrhagic Escherichia coli, Salmonella, Shigella, Campylobacter, plague, cytomegalovirus, etc. Liver function is significantly abnormal or has the following history of liver disease: AST or ALT is higher than 2 times of the upper limit of normal value, history of liver cirrhosis and hepatic encephalopathy, history of esophageal varices or history of portal shunt. There is evidence of renal function damage or the following history of kidney disease: serum creatinine is 1.5 times higher than the upper limit of normal value; History of dialysis; Or a history of nephrotic syndrome. Patients with various acute infections, tumors, severe arrhythmia, mental system disorders, and drug or alcohol addicts. History of abdominal surgery (except appendicitis, cholecystitis, caesarean section and hysterectomy). Those who were allergic to capsule drugs or contraindications. Lactose intolerance. Clinical researchers who are engaged in other related irritable bowel syndrome at the time of enrollment or within 3 months before enrollment. It is difficult to complete the follow-up, or various factors affecting the compliance. Pregnant or lactating women.