Uterine rectal fossa fluid, also known as pelvic fluid, has both physiologic and pathologic causes. Physiologic causes, that is to say, not necessarily caused by disease, are mostly seen around ovulation or menstruation, and a small amount of fluid in the rectal fossa of a woman, not more than 1cm, is a normal physiologic phenomenon, not accompanied by abdominal pain, abdominal distension, and does not require any treatment. Uterorectal fossa effusion may also be seen in pathological effusion, pathological effusion depends on the nature of the effusion, if it is a bloody effusion, it is considered to have intra-abdominal hemorrhage caused by the uterorectal fossa bloody effusion. If it is pus, it may be pelvic pus, purulent secretions accumulating in the uterorectal fossa due to severe inflammation of the pelvis. There is also the possibility of exudative fluid, but in larger amounts, with abdominal pain and bloating, consider chronic pelvic inflammatory exudate, which also requires active treatment.