Fluid in the uterine cavity may be caused by residual menstrual blood or post-abortion residues, or by uterine cavity disease. The female uterine cavity is connected to the outside world via the cervix and vagina, and to the pelvic and abdominal cavities via the fallopian tubes, so it is susceptible to diseases of the lower reproductive tract and pelvic and abdominal cavities in addition to diseases of the uterus itself. In women with poor menstrual flow or cervical adhesions, poor contraction of the uterus after abortion, and inability to drain fluid from the uterine cavity, dense fluid with light spots can be observed under ultrasound. If the lower genital tract infection or pelvic infection causes endometrial inflammation or endometrial tuberculosis, it may cause the collection of purulent exudate in the uterine cavity, and the patient is often accompanied by abdominal pain, fever or other systemic symptoms. Uterine drainage or aspiration is preferred to drain the fluid out of the body, and bacterial culture and drug sensitivity tests are feasible if the fluid is pus.