Perianal necrotizing fasciitis (PNF) is a special type of infection that typically involves mixing infection with a variety of bacteria, including anaerobic and aerobic bacteria. PNF infection can spread along the superficial fascia of the perianal and perineum, up to the abdominal wall and down to the lower extremities. Meanwhile, the infection may also spread deep to the pelvic extraperitoneal space such as the superior levator anal space, the peribladder space, the retrorectal space, and even further spread to the retroperitoneal space. These infections often spread along the fascia, the fascial space, and can also spread along the vascular and nerve crossing foramen. Although the current medical level has been greatly improved and developed, clinicians still face great challenges in the diagnosis and treatment of perianal necrotizing fasciitis. The purpose of this study was to retrospectively analyze the anatomical knowledge of perianal perineum, pelvic cavity, retroperitoneal fascia and space, as well as the infection spread and dissemination route of PNF through gross anatomical data, case data and previous literature, in order to provide reference for the diagnosis and surgical treatment of PNF.