Visual observation usually cannot determine whether an anal fistula is complex or simple. Anal fistula can be divided into simple anal fistula and complex anal fistula, can be observed through the naked eye on the perianal skin of the number of external openings to determine the rough, but the results have a certain degree of error. By observing the number of external orifices can not clarify the nature of anal fistula, to determine the type of anal fistula also need to be combined with anoscopy, the use of a probe to explore the fistula fistula; or MRI scanning can also show the location of the fistula internal orifice and the number of. Fistula often can not be self-healing, repeated episodes will lead to rectal perianal tube abscess or even cause cancer, repeated episodes of abscess will make simple fistula become complex fistula. Complex anal fistula surgery is difficult, high recurrence rate and easy to damage the anal function, so once the diagnosis is clear, should be actively treated to avoid further development of the condition, seriously affect the prognosis, should pay more attention to this disease.