Posterior fornix mostly refers to the posterior vaginal fornix. The vaginal fornix refers to the circumferential hidden fossa between the cervix and the vagina. The vaginal fornix can be divided into four parts according to its location, i.e., anterior, posterior, and lateral parts, among which the posterior vaginal fornix is located in the deepest part of the vagina, where the medication is administered to facilitate the absorption of the medication. In addition, male semen is also stored here. The posterior vaginal fornix is usually chosen as the puncture point when diagnosing bleeding from ruptured ectopic pregnancy, exudation of pelvic inflammatory fluid, or abdominal bleeding caused by other reasons. Therefore, the posterior vaginal vault is a relatively important anatomical landmark.