There are many causes of high complexity anal fistula, the details of which are as follows: 1, perianal abscess caused by repeated attacks. The causes of perianal abscess include forceful defecation, feces through the anal sinus into the intestine caused by local infection, the development of abscesses, prolonged and finally the formation of anal fistula; 2, perianal inflammatory disease, such as proctitis, ulcerative proctitis and other stimuli caused by. Anal fistula is the sequelae of perianal abscess, and perianal abscess is the acute phase of anal fistula, which are complementary and interrelated.