There is a small amount of ascites in the normal abdominal cavity, and its function is to lubricate and protect the surface of the organs in the abdominal cavity, especially to lubricate the peristalsis of the c-tube. The pelvis is the lowest part of the abdominal cavity, so it is completely normal for a small amount of ascites to accumulate at the bottom of the pelvis, sometimes up to tens of milliliters or hundreds of milliliters, so a small amount of pelvic fluid is visible during ultrasound. Some malignant tumors and more serious pelvic and abdominal inflammatory diseases can also produce more ascites or a large amount of ascites, but often accompanied by clinical symptoms and signs. Therefore, if there are no corresponding clinical symptoms and signs, it is inappropriate to diagnose pelvic inflammatory disease based on a small amount of pelvic fluid on ultrasound alone, not to mention the need for anti-inflammatory treatment.