1.Patients with unexplained blood in stool, chronic diarrhea or constipation. 2.Patients with unexplained anemia. 3.Unexplained abdominal mass or lower and middle abdominal pain cannot exclude lesions of the large intestine and terminal ileum. 4.Suspected benign or malignant tumor or chronic intestinal inflammatory disease, X-ray or CT cannot confirm the diagnosis. 5.Abnormalities are found in barium enema and other examinations, and the nature and scope of lesions need to be further clarified. 6.Determine the scope of lesions before surgery for colon cancer, review and follow-up of the efficacy after surgery for colon cancer and intestinal polyps. 7.Low-grade intestinal obstruction of unknown cause.