The anal fissure surgery 20 days still feel anal swelling may be due to ulcerative colitis, rectal mucosal prolapse, anal fissure recurrence and other reasons. 1. Ulcerative colitis: ulcerative colitis is caused by swelling and edema of the mucous membrane due to local inflammation, which usually results in abdominal pain, blood in the stool, vomiting and other symptoms, as well as a feeling of anal swelling, and ulcerative colitis can recur. 2. Prolapse of rectal mucosa: Due to the loose and prolapsed rectal mucosa, which accumulates in a certain place in the rectum, usually there are symptoms such as difficulty in defecation, dryness of stool, constipation, etc., which can also cause symptoms of anal swelling. 3. Anal fissure recurrence: patients may not want to defecate because of psychological fear of pain, which may cause constipation, and constipation may cause dryness of stools, which may aggravate anal fissure and form a vicious circle, leading to recurrence of anal fissure. Usually there will be anal itching, blood in the stool, anal swelling and other symptoms. It is recommended that patients should have regular checkups, and should pay attention to a light diet, eat more vegetables and fruits, avoid spicy and stimulating foods, and also pay attention to anal hygiene, regularly wash with warm water, drink more water, and develop good defecation habits. To sum up, patients should first go to the hospital in time to improve the relevant examination, to clarify the cause of the disease, according to the cause of the standardized treatment, to avoid aggravation of the condition.