Most patients with acute or chronic diarrhea can be clearly diagnosed based on history, signs and necessary laboratory tests, such as stool routine and culture, etc. When the diagnosis cannot be made after general routine examination, further examination should be considered, but since there are many items available for examination, the choice must be made by combining the characteristics of diarrhea in each case. Laboratory tests: 1. Stool examination: bleeding, pus cells, protozoa, worm eggs, fat droplets, etc. 2, blood tests: hemoglobin, leukocytes and their classification, etc. are helpful in the diagnosis of chronic diarrhea. 3.Small intestine absorption function measurement: it shows intestinal malabsorption. 4.X-ray and endoscopy: detect the location of lesions, motor function status, gallstones, etc. 5.B ultrasound imaging. 6.Small intestine mucosal biopsy. 7.Plasma hormone and media determination: important for the diagnosis of secretory diarrhea. 8.Endoscopy: colonoscopy and biopsy can detect colon tumor, inflammatory bowel disease, radiation enteritis, ischemic enteritis and intestinal specific inflammation, etc. Ancillary examinations: 1.Anal finger diagnosis: simple and easy, most of rectal cancer is in the rectum, which can be palpated by anal finger diagnosis, so it is very meaningful to diagnose rectal cancer. 2.Sigmoidoscopy: simple and easy to perform, only 5 minutes for one examination, less painful, can directly see intestinal mucosal lesions, and can take intestinal mucosal biopsy and make intestinal swab bacterial culture during the examination, with high positive rate, so it is significant for differential diagnosis. 3, fiberoptic colonoscopy: can be seen from the anus to the ileocecal part, clear vision, comprehensive and direct examination, can find relatively minor and small lesions, can take film, film video, is the most meaningful differential diagnosis method, is recommended. At present, fiberoptic colonoscopy is more popular nationwide. Some patients feel obvious abdominal pain during the examination, which occasionally induces coronary heart disease or leads to intestinal perforation, but it can be avoided as long as the operator is meticulous. 4, barium enema: some patients, intestinal stenosis or spasm, the intestinal cavity is not easy to pass, the need for barium enema. It can observe the whole colon lesion, and barium enema is safer and less painful, which can make up for the shortage of fiberoptic colonoscopy.