Anal swelling stool with blood and mucus is considered to be related to bacillary dysentery, ulcerative colitis, anal fistula, intestinal malignant tumors and other causes. 1. Bacterial dysentery: due to dysentery bacilli invade the intestinal mucosa epithelial cells and lamina propria, will cause inflammatory reaction and small blood vessel circulatory disorders, resulting in intestinal mucosa ulceration, congestion, edema, a large amount of exudate and other changes, so there will be anal distention and stool blood mucus symptoms. 2. Ulcerative colitis: due to some reasons caused by persistent inflammation of the intestinal mucosa, and the barrier function is damaged, which leads to intestinal mucosa erosion, ulceration, and the site of the disease often occurs in the sigmoid colon and rectum, so there will be anal distension and stool blood mucus. 3. Anal fistula: anal fistula can cause anal distension if perianal abscess is formed. When the mucous membrane of the anal fistula appears to be damaged, the capillaries will rupture, there will be repeated small amounts of purulent, bloody, mucous secretions and other manifestations. 4. Intestinal malignant tumor: common colon cancer, rectal cancer and other intestinal malignant tumors due to the repeated stimulation of intestinal mucosa by cancerous tissues will cause intestinal mucosa ulceration, congestion, edema and other changes, so there will be anal distension and blood mucus in stool symptoms. The symptoms of anal distension and bloody mucus in stool may be caused by other reasons, so it is necessary to go to the hospital in time to check the specific reasons and give treatment to avoid delaying the condition.