Generally, normal colonoscopy can exclude intestinal cancer, but there are very few cases that normal colonoscopy cannot completely exclude intestinal cancer, as follows: 1.It can exclude intestinal cancer: at present, colonoscopy is a common clinical auxiliary examination, which is mainly used to diagnose some intestinal diseases, such as chronic enteritis, bleeding intestinal ulcer, intestinal tumor, etc. Especially for intestinal cancer, colonoscopy is a very important auxiliary examination. Especially for intestinal cancer, colonoscopy is a very important auxiliary examination, and taking tumor for pathological examination under colonoscopy is the gold standard of intestinal cancer diagnosis. 2. Can’t exclude intestinal cancer: In rare cases, such as intestinal cancer is still in relatively early stage, intestinal tumor is relatively small and may grow in the muscular layer of intestine. In such cases, colonoscopy cannot see the existence of tumor and may miss the diagnosis of intestinal cancer. Therefore, in general, colonoscopy can exclude bowel cancer in most cases, but in very few cases, it cannot exclude bowel cancer completely.