Occasional stinging pain at the external opening twenty days after anal fistula surgery may be a normal phenomenon, or it may be related to perianal abscess, incomplete drainage, recurrence of anal fistula and other conditions. 1. Normal phenomenon: due to the anal fistula surgery process will leave a wound, the wound recovery takes some time, in the recovery process, there will be oozing, bleeding and pain and other phenomena. If the patient’s physical recovery ability is poor, it may take about a month for the pain to disappear. 2. Perianal abscess: If there is no active change of medicine during the recovery period, the tissue of the epidermis heals earlier, while the inside of the wound is not completely healed, which will lead to acute perianal abscess and cause pain. 3. not completely drainage: if in the process of treatment, not completely the abscess part of the complete cut clean pus, there may be drainage is not smooth, not completely drainage and other phenomena, and then appear pain. 4. anal fistula recurrence: if accompanied by the phenomenon of pain and moisture around the anus, need to consider anal fistula has recurred. It is recommended that patients seek timely medical examination, clear diagnosis, and then appropriate treatment to avoid delays.