Hemorrhoid surgery has been involuntarily shrinking the anus after the reason is the postoperative anus outside the wound is mostly open, there may be infection or postoperative perianal injury will stimulate the perianal nerve, resulting in perianal sphincter contraction caused by. 1. the emergence of infection: after hemorrhoid surgery, the wound outside the anus is generally kept open, in order to avoid wound infection, need to maintain local cleanliness and hygiene, every day on time for its care and change of medicine, can effectively reduce the risk of infection. If the care is not appropriate, when the local infection, inflammatory substances may stimulate the perianal nerve, will lead to the occurrence of anal retraction. 2. Surgical trauma: hemorrhoid surgery will have trauma to the perianal nerves, so that the nerves innervating the perianal sphincter have been in a state of excitement, resulting in involuntary anal contraction. After hemorrhoid surgery persistent shrinkage of the anus, there may be other reasons, it is recommended to go to the hospital as soon as possible to review, improve the relevant examination, clear condition, follow the doctor’s instructions in the guidance of a professional doctor to carry out the appropriate treatment.