1, abortion, post-medical abortion, clearance surgery, IUD, IUD removal and various intrauterine surgery, the most common. Postpartum, cesarean delivery is prone to occur. 2, menstruation or menstruation is not completely clean intercourse. 3, unclean sexual intercourse. 4, gonorrhea, chlamydia, mycoplasma upstream infection. 5.Adjacent organ infection (appendicitis, peritonitis). 6, systemic infection (sepsis, bacteremia). 7, perimenopause or menopause prone to bacterial infections prone to occur. 8.Patients with long-term irregular vaginal bleeding and menstrual irregularities are prone to occur.