Darkening of the intestines may be caused by insufficient blood supply to the intestines, colorectal melanosis, or malignant tumors of the colon. 1. Insufficient intestinal blood supply: Insufficient intestinal blood supply, not an independent disease, may be a symptom caused by other diseases. Insufficient blood supply to local tissues may lead to blackening of intestinal tissues, which may be a symptom of intestinal necrosis. 2. Colonic black change disease: long-term constipation, chronic intestinal inflammation, long-term use of laxatives, may form colonic black change disease. Patients mainly manifest abdominal distension, pain, constipation, defecation discomfort and other symptoms. 3. Malignant tumor of colon: If malignant tumor of colon is not treated in time, the tumor gradually increases to cause intestinal obstruction, resulting in darkening of intestinal tract. The darkening of the intestines indicates that the patient’s situation is more serious, it is recommended to clarify the cause of the disease, combined with the doctor’s advice as soon as possible to avoid serious harm.