Mobile turbid percussion is a common clinical method to check whether there is fluid in the abdominal cavity. The principle is that when there is more fluid in the abdominal cavity, more than 1000ml, when the patient is in the supine position, the fluid is concentrated in the lower part of the abdominal cavity due to gravity, and the intestinal tube containing gas floats on it, so the percussion is bulging in the middle part of the abdomen and turbid on both sides of the abdomen. When the patient is lying on his side, the fluid accumulates in the lower part and the intestinal tube floats upward, so the lower abdomen turns into turbid sound and the upper abdomen turns into drum sound, so a positive mobile turbid sound indicates the accumulation of fluid in the abdominal cavity. The examination starts from the umbilicus and percusses to the left until a turbid sound appears, the percussion trigger finger does not move, the patient is asked to lie on the right side and percusses to the right until a turbid sound appears, then the patient is asked to lie on the left side, the plate finger does not move and then percusses to the left. The free surface of the abdominal cavity was greater than 1000 ml to be meaningful.