The normal pleura can be divided into the dirty layer and the wall layer, and the dirty layer and the wall layer of the pleura migrate to each other, forming two closed cavities called pleural cavity. Due to the elastic retraction force of the lung, the pressure in the pleural cavity is lower than the atmospheric pressure, which is negative pressure. The negative pressure in the pleural cavity has important physiological and pathological significance: First, the negative pressure in the pleural cavity facilitates the expansion of the lung, facilitates pulmonary ventilation, and reduces pulmonary atelectasis and other conditions. Second, the negative pressure in the pleural cavity has a certain beneficial effect on the circulatory system. The negative pressure in the pleural cavity facilitates the reflux of the upper and lower vena cava and lymph, reducing the occurrence of pleural effusion and cardiac insufficiency. Third, when gas and liquid enter the pleural cavity, the negative pressure in the pleural cavity disappears and pulmonary atelectasis occurs, affecting cardiac function and other conditions, then it is necessary to promptly puncture, or even closed chest drainage, to restore the negative pressure state of the chest cavity as soon as possible.