The human pelvis has a certain amount of secretions that lubricate and nourish the pelvic organs, which can be divided into physiological pelvic fluid and pathological pelvic fluid according to the cause of pelvic fluid. Physiological pelvic effusion is the normal presence of exudate resulting in a small amount of exudate at the bottom of the pelvis, while pathological pelvic effusion is caused by inflammation and other factors, which is the presence of inflammatory exudate in the pelvis, and if left untreated, can slowly increase, causing symptoms such as lower abdominal cramps and pain, and in severe cases, can lead to abnormal pelvic organ function. The most common cause of pathological pelvic effusion is gynecological infectious diseases such as pelvic inflammatory disease and adnexitis, and the causes of these gynecological infectious diseases are mostly related to patients’ poor hygiene habits, such as menstruation, postpartum intercourse, inappropriate use of sitz baths and tub baths. Poor disinfection of gynecological procedures such as abortion and induction of labor, and lack of proper postoperative care can lead to gynecological organ infections, which can cause pelvic effusion. Some patients are caused by pelvic organ tuberculosis or tumor, and a few are caused by ectopic pregnancy rupture, corpus luteum rupture, pelvic abscess, chocolate cyst, and ovarian cancer. Therefore, if pelvic effusion is found in the ultrasound examination, you should let the gynecologist make a comprehensive assessment first. If it is a small amount of physiological pelvic effusion, it is not relevant and is normal, but if the amount of pelvic effusion is large, then further examination should be conducted to clarify the cause of pelvic effusion and treat it accordingly to prevent the occurrence of pelvic organ adhesions, leading to infertility and other adverse consequences.