Colonoscopy is the preferred method of examination for lesions of the cecum, colon and rectum. Patients with the following symptoms need colonoscopy: diarrhea, constipation, abdominal pain, abdominal mass, blood in stool, emaciation, anemia and other symptoms of unknown origin; barium enema X-ray with strictures, ulcers, polyps, carcinomas, diverticula and other lesions that need further confirmation; metastatic cancer, elevated CEA, CA199 and other tumor markers that need to find the primary lesion; diagnosis and follow-up of inflammatory bowel disease; preoperative confirmation of colon cancer, postoperative follow-up, post-polyp removal; endoscopic hemostasis, polyp removal, rectification of intestinal entrapment, and postoperative follow-up. Post-operative follow-up, post-polyp removal follow-up; endoscopic hemostasis, polyp removal, rectification of intussusception, intestinal torsion, dilatation of intestinal stenosis and stent placement to relieve intestinal obstruction.