An anal fistula is a fistula that is formed after an anal abscess is cut and drained or breaks down on its own, and the ulcer is the same as the anorectal canal over time. Because pus and blood often leak from the fissure, it used to be called “anal leakage”. Since most fistulas are caused by abscesses next to the anus, treatment of abscesses should take into account the effect of the treatment method on the formation of fistulas later. The principle of treatment for abscesses is to “drain the pus” and to drain the small amount of pus so that it does not get deeper and deeper and the pain of the mass increases. Due to the unique physiological structure of the anus, paranal abscesses are often treated in the same way as abscesses in other parts of the body, such as the simple application of antibiotics to control the infection, which is often counterproductive and may cause simple lesions to expand and spread, resulting in the later formation of complex anal fistulas. In contrast, choosing minimally invasive methods of drainage and patency can often reduce the chance of an abscess forming an anal fistula or allowing a larger abscess to form a simple anal fistula. Preoperative examination is particularly important to properly manage and treat anal fistulas once they have formed. The focus of the preoperative examination is to clarify the morphology of the fistula and the distribution of the alignment. Once the location of the fistula is known and the relationship with the anal sphincter is known, a minimally invasive approach can be chosen to remove as much of the tube as possible while trying not to damage the anal sphincter. The shape and alignment of the fistula can usually be determined by endorectal ultrasound or perianal MRI. In addition, preoperative colonoscopy is also important, mainly to see whether the intestine has Crohn’s disease, etc. If the anal fistula is a complication of Crohn’s disease, then the treatment of this anal fistula is very different from conventional surgery, and generally difficult to cure.