Some elderly people with chronic diarrhea need to be alerted to colon cancer. About 60% of the clinically diagnosed colon cancer patients had suffered from colitis. There is a quantitative to qualitative process from colitis to colon cancer, and the risk of colon cancer is as high as 40% for patients with colitis. Older patients with chronic diarrhea tend to take this chronic process lightly. The initial symptoms are not significantly different from those of ordinary diarrhea, and early symptoms such as bloating and indigestion may be present, which can often be relieved by general treatment. Later, changes in bowel habits may occur, such as increased frequency of constipation, diarrhea or constipation, abdominal pain before stool, and later mucus stool or mucopurulent blood stool. When the size of the tumor increases and affects the passage of feces, diarrhea and constipation may occur alternately. The bleeding volume of right hemicolectomy is small, and it is not easy to be seen by the naked eye because it mixes well with the stool with the peristalsis of the colon, but the occult blood test is often positive. When the cancer is located in the left hemicolectomy, blood and mucus are not mixed with the stool because the stool tends to form, and fresh blood and mucus can be seen in the stool of about 25% of patients. The early symptoms of colon cancer are light or not obvious, which are often ignored by patients and easily missed. Therefore, patients above middle age should be more alert when the above symptoms appear and consider the possibility of colon cancer. They should actively go to hospital to improve rectal diagnosis, colonoscopy, barium enema and tumor markers to achieve early detection and treatment and improve life quality.