The posterior fornix is the part of the vagina near the rectus uteri recess. The crypt between the vagina and the cervix is the part of the vaginal fornix, which is divided into four parts according to its position: anterior, posterior, left and right. The posterior fornix is the deepest and is in close proximity to the uterorectal recess, which can be used as an entry point for puncture and surgery. When hemorrhage, fluid accumulation, or pus accumulates in the abdominal or pelvic cavity, it tends to collect in the lowest part of the pelvis, and aspiration of pelvic fluid from the posterior fornix can be used as a clinical diagnosis method. In the case of pelvic pus, puncture and drainage of the posterior fornix can be used as a therapeutic access for pelvic pus; in the case of endometriosis, palpation of painful nodules in the posterior fornix can assist in the diagnosis of endometriosis. If there is any abnormality in the posterior fornix, it is necessary to consult the doctor in time, improve the examination under the doctor’s guidance, make a clear diagnosis, and give appropriate treatment.