The large intestine is about 1.5 m long and is in the abdominal cavity in an approximate “? shape around the small intestine. The large intestine includes the colon and the rectum. Depending on the location of the colon, the colon can be divided into cecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon and sigmoid colon. The large intestine is connected to the small intestine above and to the anal canal below, and is connected to the outside world through the anus. Therefore, we can insert a colonoscope through the anus to examine and treat many diseases of the large intestine. The large intestine is distributed in the shape of a “portal” around the stomach, covering almost the entire abdominal cavity. In the center of the large intestine is the small intestine, above it are the liver, gallbladder, bile ducts and stomach, to the upper left is the spleen, behind it are the large blood vessels, kidneys and ureters, and below it are the uterus, ureters and bladder. Because of the close proximity of the colon to these organs, lesions of the colon are sometimes difficult to distinguish from lesions of these organs. For example, many patients with colorectal cancer are often misdiagnosed as gastric disease, and many patients with liver cancer are misdiagnosed as colitis. Therefore, in order to accurately diagnose colorectal diseases, colonoscopy must be performed as early as possible.