Prolapse is caused by continuous increase of intra-abdominal pressure, diarrhea, pelvic anatomical problems and so on. 1. Continuous increase of intra-abdominal pressure: if the patient is constipated, the stool is too hard or too little, it is difficult to discharge, and defecation is less than 3 times a week, when defecation will be downward force, the front wall of the rectum will move downward and protrude into the rectum under the pressure of the external force, when the intra-abdominal pressure continues to increase, the front wall of the rectum will be deepened with the deepening of the depression downward sliding, and gradually prolapse from outside the anus. 2. Diarrhea: if the patient has diarrhea, the stool is watery or thin, defecation more than 3 times a day, it will make the local mucous membrane of the anus loose, and the mucous membrane will be loose due to the role of gravity or the patient’s physical weakness and prolapse out of the anus. 3. Pelvic anatomical problems: including perirectal fascia laxity and lack of fixation mechanism, bladder (or uterus) rectal fossa position is low, the sigmoid colon is long, the pelvic floor muscle weakness, or pelvic surgical history, etc., can cause prolapse of the anus. To summarize, the causes of prolapse are many and complex, it is recommended to go to the regular hospital in time for a clear diagnosis and reasonable treatment.