Anal fistula surgery done the first day without pain, may be related to anesthesia drugs, different pain nerves, low anal fistula and so on. 1. Anesthesia drugs: before anal fistula surgery, patients will be injected with anesthesia drugs, surgery under anesthesia. Anesthesia drugs in the body to fully metabolize need a certain time, if the patient’s anesthesia drug is not fully metabolized, the patient temporarily do not feel the pain of the wound. 2. Different pain nerves: each person’s sensitivity to pain is not the same, there are also patients after surgery, do not feel the pain, not only for anal fistula surgery, do other small surgery experience is similar. 3. low anal fistula: if the patient belongs to the low anal fistula, due to this part of the muscle tissue is not a lot, coupled with the hanging line on the local damage is not very big, so the patient feels not much pain. It is recommended that after the operation, the patient will promptly inform the doctor of their own experience, necessary communication, may need to carry out the appropriate examination and treatment.