Many people refuse to undergo colonoscopy because they are afraid of it. In fact, colonoscopy is as convenient as gastroscopy. President George W. Bush routinely underwent a colonoscopy because of colon polyps. A colonoscopy is a common member of the fiberoptic endoscope family. It is inserted retrograde through the anus to examine the rectum, sigmoid colon, descending colon, transverse colon, ascending colon and cecum, as well as a small section of the small intestine (ileocecal end) that is connected to the large intestine. Through the mirror, not only can intestinal lesions be clearly detected, but also some intestinal lesions can be treated, such as: direct microscopic removal of benign lesions such as colon polyps, microscopic hemostasis of intestinal bleeding, and removal of foreign bodies from the large intestine. Colonoscopy is the main tool that cannot be replaced by other treatment methods. Before the colonoscopy, you only need to eat a liquid or semi-liquid diet 3 days before the examination, fast in the morning of the examination, and take a laxative such as mannitol the night before the examination to cleanse the intestine so as not to affect the observation and operation, or clean enema to ensure the cleanliness of the intestine. During the examination, the doctor will inject a certain amount of gas into the intestinal cavity through the colonoscope to facilitate observation. Due to the tortuous structure of the colon, the examinee may experience varying degrees of distension or pulling sensation during the examination. For those who are overly nervous or have a high degree of intestinal spasm, sedatives or antispasmodic drugs are required. In children who are unable to cooperate, the test is performed under anesthesia. The gas injected is aspirated before the end of the examination and most people have no significant discomfort. If no lesion is found and no treatment is administered, the subject can move and eat normally. Fiberoptic colonoscopy can observe the location, size and morphology of intestinal lesions, and can detect early cancers below 1 cm, and can also complete whole cancer biopsy for relatively small early cancers and early cancers of the tipped type. To understand its pathological differentiation degree. Therefore, anyone who has change in stool habit, unexplained lower gastrointestinal bleeding, especially those over 40 years old, should have a routine microscopy once a year which is conducive to timely detection of precancerous lesions and early cancers such as colorectal cancer, familial intestinal adenomatosis, ulcerative colitis, etc. Don’t refuse the examination you should receive because of ignorance about it and lose the time for treatment.