The dirty and wall layers of the pleura are displaced from each other to form two completely closed cavities called pleural cavities on the left and right. The significance of the existence of the pleural cavity: First, the normal pleural cavity has a little liquid, which can reduce the friction between the dirty layer and the wall layer of the pleura during respiratory movement. Second, the pressure in the pleural cavity is called the pleural cavity pressure, regardless of inspiration and exhalation, are lower than the atmospheric pressure for negative pressure. The negative pressure in the pleural cavity plays an important role in maintaining the dilated state of the lung, ensuring normal pulmonary ventilation, and the return of venous blood and lymph to the heart. Third, in the pathological state, fluid and gas accumulation in the pleural cavity caused by a variety of reasons, resulting in the reduction and disappearance of negative pressure in the pleural cavity, or even become positive pressure when the lung and heart have certain effects. Therefore, puncture is needed to perform closed drainage of the pleural cavity and restore the negative pressure state of the pleural cavity.