High-grade complex anal fistula is a difficult disease in anorectal surgery, with complex surgery, low success rate in one operation, often requiring sub-operations, and high recurrence rate after surgery, causing long term pain to patients and embarrassment to surgeons. The treatment of anal fistula differs from other anorectal diseases in that it is characterized by the indeterminate nature of surgery, unlike hemorrhoids which have specific procedures such as open, closed, semi-open and anastomotic resection (PPH). This is especially true for the treatment of high complex anal fistulas, so that the surgeon’s experience is important. (1) Diagnostic criteria for high-grade complex anal fistula There are more than ten diagnostic criteria for anal fistula, and the ones often used in China are the diagnostic criteria for anal fistula developed by the National Anal Collaborative Conference in 1975, the Parks criteria in 1976, and the Yukio Sumikoshi criteria in Japan in 1979, which have in common the complexity of classification and poor guidance for application in specific operations. The latest edition of the American Society of Colorectal Surgeons (ASCRS) guidelines for the management of anal fistulas classifies complex fistulas as follows: those with a tube penetrating 30-50% of the external sphincter (high trans-sphincter type, extra-sphincter type, supra-sphincter type), anterior fistulas in female patients, multiple tubes, recurrent types, those with anal incontinence, radiotherapy patients, and Crohn’s disease complications. We use a simple classification, where two issues are involved: high, whether the fistula penetrates the puborectal ring; and complex, whether it has multiple external openings or multiple ducts. By Corman’s opinion, clinically, complex means that it is more difficult to manage and more likely to impair bowel control than the common anal fistula. (2) Internal orifice of high-grade complex anal fistula: Regardless of the doctrine of anal gland infection and intersphincteric abscess by surgeons such as Parks, Eisenhammer and Goligher, or the central gap doctrine as physiological anatomist Sharfik, the primary focus of anal fistula is located in the dentate line. The internal opening is still located in the dentate line. If there is an opening near the puborectal ring (not an internal opening), it is often associated with trauma (including foreign bodies, improper surgery), Crohn’s disease, and pelvic infection. The course of the fistula is consistent with Parks’ type IV-external sphincter fistula diagnosis. (3) Application of preoperative endorectal ultrasound Ultrasound is sensitive to different levels of discrimination, and preoperative endorectal ultrasound can clearly detect the course of the fistula, its relationship with the sphincter and puborectal ring, the location of the internal opening, and whether it is accompanied by local infection or even abscess formation, which is of great significance for detailed diagnosis and guidance of surgery. The drawback is that it is not possible to distinguish accurately between fistula and scar, especially in patients who have undergone anal fistula surgery, and endorectal ultrasound often suspects the healed fistula scar to be a fistula. It has been suggested that injecting hydrogen peroxide into the fistula to increase contrast would improve accuracy. The clinical application of the 10M rotating probe in recent years has resulted in a diagnostic accuracy of 81%-91% for ultrasound. (4) Application of preoperative MRI In 1992, lunniss first introduced MRI examination in the preoperative examination of anal fistula, with an accuracy rate of 88%. The role of MRI in the examination of anal fistula has been studied more in recent years at home and abroad, and it is now believed that for primary anal fistula, endorectal ultrasound can accurately identify the internal opening and canal with less cost. The diagnostic value of MRI in recurrent anal fistula is greater. We believe that the surgical treatment of anal fistula should pay attention to three points: 1) careful search and treatment of the internal opening; 2) complete incision or excision of the fistula; 3) adequate and reasonable drainage. For high-grade complex anal fistula, our experience is to cut or remove the fistula under direct vision, pay attention to protect the function of sphincter and puborectal ring, and strive to achieve a better treatment effect with less damage. (1) Application of methylene blue during surgery We believe that methylene blue staining should not be injected during surgery for high complex anal fistula because it is emphasized that surgery should be performed under direct vision, and the penetration path of high complex anal fistula is complicated and often has small branches, so it is difficult to accurately cut the main fistula at one time, and when part of the fistula is cut, methylene blue will stain the whole operation field and the opportunity to explore the fistula under direct vision is lost. The surgeon has only one opportunity to view the fistula and the internal opening before the entire mucosa is contaminated. If done blindly, an artificial tube will be formed, expanding the surgical damage and not necessarily allowing for accurate incision or removal of the fistula, which will certainly result in recurrence of the fistula after surgery. Of course, for fistulas that drain well in the natural state of the external orifice and are thick and have few branches, intraoperative injection of methylene blue stain will make the fistula visible at a glance and improve the speed of surgery. (2) Intraoperative management of the caudal ligament The caudal ligament is considered to be an important tissue that holds the anus in place, and if severed will lead to anal displacement and affect defecation. When dealing with posterior high complex anal fistula and posterior horseshoe fistula, we found that if the caudal ligament is preserved, the operation is difficult to perform, and even if the operation is barely completed, the postoperative drainage will be difficult, resulting in failure of the operation. In contrast, after cutting the caudal ligament, the drainage was clear and the surgery had a curative effect, and the patient’s anus was not significantly displaced. We considered that the scar formed in the postoperative surgical area played the role of the preoperative anal caudal ligament. (3) Application of intraoperative hanging wire Sharfik’s three-muscle loop doctrine holds that each U-shaped loop is an independent sphincter and that each loop can be individually self-made, and that surgery can cut off any of the loops without affecting the bowel control function. This doctrine is widely controversial, and we agree with clinical experts that the puborectal loop should be treated with caution, and that fistula hook-ups and staged surgery are needed if the fistula penetrates it. Another role of hanging wires is that they can provide good drainage. (4) Application of intraoperative biogel Biogel has made significant use as an effective filler in aseptic operations to speed up the healing of wounds. High complex anal fistulae have large wounds and slow healing, and people have thought of various ways to speed up the healing process, and biogel is one of them. Our experience is that the tip and blind end of the fistula can be filled with the right amount of epithelialized tissue after sufficient scratching to accelerate the healing process, but do not fill the wound completely, which will not accelerate the healing process and also affect the drainage effect. (5) Intraoperative electric knife application Foreign anal fistula surgery is generally used electric knife, the hemostatic effect of the electric knife in this type of surgery is fully reflected, and a clean field of view for direct vision to find the fistula is not beneficial. The cost is not popular in China, so we advocate it here.