Clinically, anal fistulas are generally classified into the following two categories: simple anal fistulas: are those with only one external opening in the skin next to the anus. The first national anal colloquium in 1975 established a unified classification standard for anal fistulae, which is marked by a line drawn through the deep part of the external sphincter, and the fistula is high if it passes above this line and low if it passes below this line. The classification is as follows: 1. low simple anal fistula There is only one fistula that passes below the deep external sphincter and the internal opening is near the anal sinus; 2. low complex anal fistula The fistula passes below the deep external sphincter and has more than two external openings or two or more tubes and the internal opening is in the anal sinus; 3. high simple anal fistula There is only one tube that passes above the deep external sphincter and the internal opening is in the anal sinus; 4. high Complex anal fistula with more than two external ports and ducts with branching sinus tracts, whose main tube passes above the deep layer of the external sphincter and has one or two or more internal ports. The fistulae are classified according to their relationship with the sphincter: 1) submucosal fistulae; 2) intersphincter fistulae; 3) trans-sphincter fistulae; 4) supra-sphincter fistulae; 5) extra-sphincter fistulae.