A typical anal fistula can be initially judged from its appearance because there is often one or more breaks in the skin surface around the patient’s anus and buttocks, which appear as depressions or protrusions with pus flowing out, etc. However, to make an accurate diagnosis, a combination of finger palpation, probing, staining, ultrasound and even nuclear magnetism is needed to reduce misdiagnosis or missed diagnoses. Local palpation: Palpation includes extra-anal palpation and intra-anal palpation. For superficial fistulas, palpation can often reveal the direction of the fistula, whether it is straight or curved, and if there are more than two external openings, whether there are multiple simple fistulas (each with an internal opening) or complex fistulas (many external openings and only one internal opening). Endoanal palpation is performed to determine the location of the internal orifice and to understand the degree of sclerosis of the anorectal ring. Generally, the internal orifice of an anal fistula will be sunken, raised, indurated, and hard, which is distinct from other areas. In the case of submucosal fistulae, palpation allows the length of the fistula, its course, and the presence of intestinal stenosis. For deep fistulas, it is sometimes difficult to palpate the pathway, especially for supra-pubic rectus intersphincteric fistulas, finger palpation is more difficult and often requires a combination of other tests to make the diagnosis. Probing and staining: These two methods are generally used more often intraoperatively. If the fistula is simple and straight, it is easy to detect from the external to the internal port, but if the fistula is curved or even if the fistula is complex or branched, it is difficult to use the probe to its advantage. Inject methylene blue solution or a mixture of methylene blue and hydrogen peroxide from the outer mouth to observe the stained area of the inner mouth, in addition to staining the pathway through which the stain is found to clarify the path of the fistula. Contrast method: 30% to 40% iodized oil or 60% pantethine can be used. The contrast agent is injected from the external port and the fistula is observed under X-ray and the location of the internal port. However, the disadvantage is that although the fistula is clearly visible, the perianal muscle relationship cannot be visualized, so it is not comprehensive enough and only a general judgment of the fistula can be made. Intraluminal ultrasound and endoscopic ultrasound: Intraluminal ultrasound can clearly distinguish the direction of the main fistula, the distribution and number of branches and the location of the internal orifice. Endoscopic ultrasound is a comprehensive technique that combines endoscopy and ultrasound. A miniature ultrasound probe is attached to the tip of the endoscope, which can display clear images of all levels of the canal wall and surrounding structures. Magnetic resonance imaging (MRI): MRI has high soft tissue resolution and can directly image in three dimensions (frontal, sagittal and axial), which can clearly show the course of the fistula and the relationship with the sphincter, and can accurately depict the anatomical structures of the internal and external anal sphincter, anal levator and puborectal muscles, especially the muscle images are clearer after pressing the fat. In conclusion, clinically, one or several examination methods should be selected according to the complexity of the anal fistula to make accurate judgments on the course of the fistula, the internal orifice site and the relationship with the sphincter muscle in order to accurately eliminate the lesion and reduce recurrence.