The utero-rectal fossa is the lowest point in the pelvic abdominal cavity, and when there is fluid in the abdominal cavity it will accumulate in the utero-rectal fossa, forming utero-rectal fossa fluid. At present, there are several clinical reasons for the accumulation of fluid in the uterine rectal fossa. First, pelvic inflammatory diseases. Pelvic inflammatory disease is the most common cause of utero-rectal fossa effusion, as the inflammatory reaction of female reproductive system organs can lead to the accumulation of peritoneal inflammatory exudate fluid in the utero-rectal fossa to form effusion. Second, inflammatory lesions of other organs in the abdominal cavity. When inflammatory reactions occur in the organs of the patient’s abdominal cavity, the fluid produced by them can eventually flow into the rectal fossa of the uterus to form effusion, with common diseases such as appendicitis and diffuse peritonitis. Third, traumatic diseases in the abdominal organs. When a patient suffers an external blow that causes bleeding from ruptured organs in the abdominal cavity, blood eventually flows into the utero-rectal fossa, and fluid accumulation in the pelvic utero-rectal fossa is visible under ultrasound prompting. Fourth, gynecological acute abdominal disease. Common obstetrical and gynecological diseases, such as ectopic pregnancy and corpus luteum rupture, can cause local bleeding in the fallopian tubes and ovaries, which eventually manifests itself in the form of fluid in the rectal fossa of the uterus. In summary, fluid in the utero-rectal fossa can be caused by trauma from inflammatory diseases of the pelvic and abdominal organs, bleeding from organ rupture, and common gynecological and obstetric emergencies.