The causes of pelvic fluid in unmarried women are considered in three ways: First, there may be a small amount of pelvic fluid due to ovulation with the rupture of follicles and the outflow of follicular fluid. Second, during menstruation, with the reflux of menstrual blood, a small amount of pelvic fluid may be found during ultrasonography. Third, when there is inflammation of the pelvic cavity, such as severe inflammation of the pelvis itself or of the intestinal tract, pelvic effusion may also occur. If the pelvic fluid is relatively small and the patient does not have obvious clinical symptoms such as lower abdominal cramping and discomfort, it is recommended that it can be temporarily observed. If it is accompanied by pain and discomfort in the lower abdomen, it needs to be treated systematically according to pelvic inflammatory disease or enteritis.