Tarry stool is a sign of gastrointestinal bleeding and is not a sign of cancer, but there are some malignant tumors of the digestive system that can cause tarry stool, the probability of which is about 10-30%. When the patient has tarry stool, it usually indicates that there are symptoms of gastrointestinal bleeding, especially lower gastrointestinal bleeding, and the patient can go to the gastroenterology department of the hospital for consultation. Routine stool examination, if found that the occult blood is positive, it suggests that gastrointestinal bleeding is greater than 5 milliliters, and need to be further performed gastrointestinal endoscopy. Painless colonoscopy can be given after cleansing the intestines to clarify the degree of damage to the intestinal mucosa and the cause of the bleeding, and may reveal ulcers and malignant ulcers in the intestines. It is recommended to give different treatments according to different causes, and surgery is preferred for intestinal malignant tumors.