The main symptoms of anastomotic fistula in rectal cancer are as follows: first, repeated fever, sometimes even causing persistent fever, if there is an unexplained fever, the appearance of anastomotic fistula should be suspected; second, severe anastomotic fistula will show symptoms of diffuse peritonitis, including abdominal distension, abdominal pain, and abdominal muscle tension, which are symptoms of severe anastomotic fistula; third, during the surgery, usually a The most intuitive way to determine the occurrence of an anastomotic fistula is to discharge some feces from the drainage tube. If the anastomotic fistula is diagnosed with an anastomotic defect, the anastomotic fistula will be confirmed. However, before the anastomotic fistula occurs, some patients usually present with some atypical symptoms, mainly some recurrent fevers. Such patients need some other tests, including imaging and anoscopy, to confirm whether an anastomotic fistula has occurred and to intervene early in time to prevent serious complications.