Recently, we often encounter some patients, the physician believes that there is a need for colonoscopy, but the patient just refused to do it, which eventually led to a big mistake, missed the time for treatment, and the physician can do nothing about it. Therefore, it is necessary to say more about the need for colonoscopy. Colonoscopy has been used in clinical practice for more than 40 years, the first clinical application in 1963 is fiber colonoscopy, followed by the emergence of electronic colonoscopy, which has become the most common clinical application of colonoscopy, but also the most basic inspection equipment, those who need to do colonoscopy? Common reasons are: 1, unexplained blood in the stool or positive fecal occult blood test; 2, repeated changes in stool characteristics such as diarrhea or constipation; 3, unexplained wasting and anemia; 4, repeated unexplained chronic lower and middle abdominal pain; 5, lower and middle abdominal masses; 6, the need to observe the effectiveness of treatment, such as polypectomy, inflammatory bowel disease after treatment, colon tumor surgery, etc. In recent years, with the change of people’s health consciousness and concept, the continuous improvement of instruments, the clinical insertion of mirror technology, the development of painless colonoscopy, expanding the scope of diagnosis and treatment of colon diseases, colonoscopy combined with physiological and biochemical research, has transitioned from simple diagnosis to census, so that early detection of some early cancer, precancerous lesions, etc., so that patients get timely treatment, improve the quality of life, and prolong life expectancy.