Tau fossa effusion is the presence of pelvic fluid, which accumulates mainly inside the recto-uterine sulcus. There are many conditions that can cause pelvic fluid, the most common being pelvic inflammatory disease, ovulation and pregnancy, which need to be diagnosed in conjunction with the patient’s presence or absence of other uncomfortable symptoms. If you suffer from pelvic inflammatory disease, you need timely anti-infective treatment, you also need to add anti-anaerobic drugs, because the pelvis is a low-oxygen environment, it is easy to be infected by anaerobic bacteria. You need to pay attention to keep the perineum clean and hygienic, change underwear frequently, avoid wearing tight underwear, in order to prevent the occurrence of upward infection and lead to pelvic inflammatory disease. If the effusion is due to early pregnancy or ovulation, it can be observed temporarily and does not need special treatment.