I. Medical history: constipation, chronic colitis, polyposis, especially in middle-aged and elderly patients with familial polyposis, the occurrence of stool habits and shape changes in patients should be taken seriously. Clinical symptoms: 1. change in bowel habits: rectal cancer: manifested as frequent bowel movements, increased frequency, no stool discharge or little stool quantity in the toilet, unclean feeling of defecation, often with mucus stool; stool deformation, thinning and flattening, or with grooves. Colon cancer: increased number of bowel movements, alternating diarrhea and constipation, with mucus-pus-blood stool. 2.Blood in stool: anal bleeding during defecation, mostly dark red blood, often mucus blood stool, rectal cancer patients can be fresh blood. 3.Symptoms of intestinal obstruction: mainly manifested as abdominal pain and bloating, and difficulty in stool. 4. Systemic symptoms: late stage may include wasting, weakness, anemia and other symptoms. The three examinations are endoscopy, X-ray examination and occult blood test. Anorectal diagnosis: It is the most important method to diagnose rectal cancer. Most of the rectal cancers located in the middle and lower part of the rectum can be palpated through finger diagnosis, and the size, shape, hardness, activity and distance from the anus of the mass can also be understood. 2.Endoscopy: there are proctoscopy, sigmoidoscopy and fiberoptic colonoscopy, generally, proctoscopy and sigmoidoscopy are used first, and then fiberoptic colonoscopy is performed if there is suspicion, and biopsies must be taken for pathological examination to confirm the diagnosis. 3.X-ray examination: mainly colon gas-barium enema double imaging, barium meal examination is strictly prohibited for serious obstruction. 4.Fecal occult blood test: if the occult blood test is positive, further examination should be performed, which is important for early detection of tumor.