First, gradually aggravated abdominal distension, abdominal pain: the cause is due to intestinal dysfunction, or intestinal obstruction. It is mostly concentrated in the middle and lower abdomen, mostly hidden pain or distension, and there is a tendency of gradual aggravation. Second, intermittent blood in stool: because the lesion is close to the anus, so the blood color is mostly bright red or dark red, and it is often separated from the blood. Only when there is more bleeding, the stool is brownish red and jam-like. In right half colon cancer patients, blood in stool visible to the naked eye accounts for 36.5%. Third, anemia: when long-term chronic blood loss exceeds the compensatory function of hematopoiesis of the body, the patient can show anemia, and the anemia worsens with the progress of the disease. Fourth, change of defecation habit and fecal character: patients with rectal cancer may increase the number of feces, but the number of feces each time is not much, or even there is no feces at all, only some mucus and blood are discharged, and there is the feeling of incomplete defecation. The change of stool habit and frequency, as well as constipation or unexplained diarrhea may occur only when the tumor of large intestine is relatively large and has erosion, ulcer or infection. If the cancer protrudes and grows into the lumen of the rectum, resulting in relative narrowing of the intestinal lumen, the discharged stool tends to be thin and deformed, and may be flat, and sometimes the deformed stool has some blood attached to it.