In clinical practice there are four general criteria for bowel cleanliness. Grade A refers to the absence of feces and a small amount of fluid in the patient’s intestinal tract. Grade B means that there is a small amount of stool or a small amount of fluid in the patient’s intestine, but it does not affect the observation of colonoscopy. Grade C means that there is a moderate amount of stool in the patient’s body, which can be aspirated without delaying the observation of the colonoscopy and does not affect the results. Grade D means that the patient’s intestine is not clean and a large amount of stool is present, which affects the results of the examination, and the situation in the intestine cannot be observed smoothly by aspiration of stool. If patients want to do colonoscopy, they can try to excrete the feces and mucus in the intestine, so that the observation of the intestine can be facilitated.