Colonoscopy is the most effective means of detecting early lesions of the colorectum. The colorectum is about 1.5m long and forms a box around the jejunum and ileum. According to the location and characteristics of the large intestine, it is divided into ileocecal, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal, so what is their normal shape under colonoscopy? Normal rectum: 12-15 cm. without semilunar folds, with three Hentu flaps. Normal sigmoid colon: 15-30 cm, often crescent-shaped or oval, with a slightly rough mucosal surface, round-like folds, low and dense, and a tortuous and variable intestinal lumen. Normal descending colon: 30-40 cm. the intestinal lumen is cylindrical or upright equilateral triangular, rarely curved, and the view is deeper and wider. The semilunar folds are clearly visible and evenly divided. Normal splenic flexure: 40-45 cm. sharp curves going to the left, with elevated higher semilunar folds seen on the left and deeply concave colonic pockets on the right. The mucosa is smooth and lustrous, with clear vascular texture. A circular light blue spleen pressure mark is visible in the splenic flexure in about half of the patients, especially in those with enlarged spleens, and the rest of the mucosa is light orange-red. Normal transverse colon: 40-60 cm. after inflation, a wide mucosal fold surrounding the intestinal lumen is visible, forming a complete inverted triangle with uniform divisions of triangles. Normal hepatic flexure: 55-60 cm. an arcuate fold is often seen at the junction of the hepatic flexure and the transverse colon, with the concave surface toward the patient’s dorsal side; the hepatic flexure is also in the shape of a blind pouch, mostly close to the liver, and the corresponding intestinal lumen is visible as a light blue, sharply margined projection of the indentation of the liver. Normal ascending colon: 60-80 cm. The lumen of the ascending colon is also triangular, but in contrast to the transverse colon, it is orthotriangular; the mucosa is light orange-red, and the submucosal vascular texture is not as clear as that of the descending colon. The semilunar folds are the most prominent, and the colonic pouch is the deepest. Normal ileocecal part: 70-90 cm. ileocecal part includes cecum and ileocecal flap, which is the part below the ileocecal flap and the semilunar folds extending from both sides, in the shape of a blind capsule, and an incomplete longitudinal fold can be seen in its anterior wall; the opening of the appendix can be seen in the middle of the cecum, resembling a diverticulum or semilunar-like, and the ileocecal flap is located at the medial edge of the ascending colon and the displaced part of the cecum, in the shape of a mouth and lips, and also in the shape of a papilla or a mass-like protrusion.