Diarrhea is divided into acute diarrhea and chronic diarrhea, and the difference between acute and chronic diarrhea is the length of time. In general, the duration of acute diarrhea does not exceed three weeks, while chronic diarrhea is more than one month. Acute diarrhea may be caused by intestinal infections, non-infectious lesions of the intestine such as acute hemorrhagic necrotizing enterocolitis, acute poisoning, systemic diseases, laxatives, functional diarrhea, and psychiatric factors. And chronic diarrhea may be caused by diseases of the digestive system such as gastric diseases, intestinal infections, intestinal tumors, inflammatory bowel disease, small intestine malabsorption; systemic diseases including endocrine and metabolic disorders and other systemic diseases; drugs such as laxatives; and intestinal disorders. The mechanism of diarrhea is very complicated, so to clarify the cause of the onset of the disease must be confirmed through relevant examinations, and cannot rely on a single way to diagnose. 1.Inquiry into medical history: including the patient’s age, gender, onset, duration, number of diarrhea, nature of stool, accompanying symptoms, etc. 2.Physical examination: observe whether the patient has obvious symptoms such as wasting, ascites, jaundice, arthritis, etc. In addition, it is also necessary to perform anal finger examination. 3, stool test: stool test can indicate the nature and location of intestinal lesions. 4, endoscopy: for patients with long-term diarrhea, colonoscopy should generally be taken. Colonoscopy can effectively and intuitively observe the situation of the intestine, and the diseased tissues can be removed and pathological examination can be done in time, which can identify intestinal inflammation or tumor masses more quickly, and is extremely useful for distinguishing the pathogenesis of inflammatory diseases. Diarrhea caused by gastric cancer is different from other chronic diarrhea. Diarrhea caused by stomach diseases is often accompanied by upper abdominal pain and usually does not cause constipation, and patients with long-term diarrhea should undergo gastroscopy to exclude stomach diseases.