There are more reasons for diarrhea in late stage of colon cancer, as follows: 1, dysbiosis: the most common. Due to chemotherapy or other treatments in late stage of colon cancer, it causes damage to intestinal mucosa, and after the damage, it causes dysbiosis, which eventually causes diarrhea; 2, drug side effects: for example, common chemotherapy drugs, most of them will cause diarrhea; 3, malnutrition: it causes dysfunction of digestive tract, which will also cause diarrhea. Therefore, diarrhea in advanced patients should be considered from many aspects, first analyze the cause and catch the main contradiction to deal with it. Microecological treatment or antidiarrheal drugs can be used, while reducing the application of drugs that cause diarrhea to achieve the purpose of treating diarrhea in advanced patients.