Inclusion Criteria:  Meet the AIS diagnostic criteria; Age 18-80; Within 7 days of the onset; Signing the informed consent, providing relevant medical history and biological specimens.  Exclusion Criteria:  mRS > score 2 before onset; Serious systemic diseases including malignant tumors; Hematological diseases and autoimmune diseases; ALT or AST > 2 times the upper limit of normal value or severe liver disease; Serum creatinine > 1.5 times the upper normal limit or severe nephropathy; History of alcoholism, drug abuse, and chemical poisoning (e.g. pesticide poisoning); History of intestinal tumor, irritable bowel syndrome or inflammatory bowel disease or confirmed in hospital; Antibiotic use within 1 month before admission; Fece cannot be obtained within 4 days after admission.