The brown color of stool after anal fistula surgery may be related to the overflow of secretion at the wound, wound infection, other diseases and other conditions. 1. Wound secretion overflow: anal fistula consists of three parts, namely the internal mouth, external mouth and fistula, after surgery, the part will leave a wound, the wound recovery process, there will be blood and secretion overflow, which is a normal phenomenon. In the process of bowel movement, such blood or secretion mixed with stool discharge, it looks like brown stool. 2. Wound infection: If there is more blood or other mucus tissue sticking on the stool, and it is not relieved for a long time, accompanied by pain in the anal area, fever and other symptoms, you need to consider the possibility of wound infection. 3. Other diseases: if the patient has gastric diseases, such as duodenitis, gastric ulcer, etc., there will be bleeding in the lesion area, and the stool will be brown when the blood is mixed with the stool. If the patient has intestinal tumors, the tumor material ulcers bleeding, will also cause stool color change. As the causes of the above cases are many, if accompanied by other uncomfortable symptoms, it is recommended that the patient should consult a doctor in time for a detailed examination and a clear diagnosis, and then follow the doctor’s instructions to give reasonable treatment to avoid delaying the condition.