Early colorectal cancer has no obvious symptoms, and clinical symptoms appear only when the disease has developed to a certain degree, mainly in the following five aspects: 1, bowel irritation symptoms and change in bowel habits: frequent stools, diarrhea or constipation, sometimes alternating constipation and diarrhea, urgency, anal swelling, accompanied by vague abdominal pain. Older patients are unresponsive and insensitive to pain. Sometimes, they may feel abdominal pain only after perforation or peritonitis has occurred. 2.Blood in stool: the tumor breaks down and bleeds, sometimes bright red or darker, generally the bleeding amount is not much and appears intermittently. If the location of tumor is high, blood mixed with stool will be jam-like stool, sometimes mucus blood stool. 3.Intestinal obstruction: Intestinal obstruction is a manifestation of late stage colon cancer, and left-sided colonic obstruction is common. The obstruction caused by ulcerative or hyperplastic colon cancer spreading around the intestinal wall and infiltrating into the intestinal lumen narrowing is often chronic incomplete mechanical intestinal obstruction, with abdominal distension, abdominal discomfort, then paroxysmal abdominal pain, hyperactive bowel sounds, constipation or thin stool (pencil shape, sheep stool shape) to stop defecation and exhaustion. Acute intestinal obstruction is mostly caused by infiltrative colon cancer, and there are many elderly patients with intussusception and intestinal obstruction caused by tumors, so we should be alert to the possibility of colon cancer for elderly people with intussusception. No matter acute or chronic intestinal obstruction, the symptoms of nausea and vomiting are not obvious, if there is vomiting, the small intestine may have been invaded by tumor. 4. Systemic toxic symptoms such as anemia, emaciation, fever and weakness: due to tumor growth consuming nutrition in the body, long-term chronic bleeding causes anemia and tumor secondary infection can cause fever and toxic symptoms.