The normal value of pleural cavity pressure is -4 to -6 cm water column. The pleural cavity is a closed cavity enclosed by the dirty pleura and the wall pleura. When the lungs are breathing, a negative pressure in the pleural cavity occurs, which generally keeps the lungs in a reopened state and facilitates gas exchange. When there is gas in the alveolar rupture pleural cavity, it will compress the lung and form positive pressure in the chest cavity, which will further compress the lung and cause pneumothorax. When the amount of pneumothorax exceeds 30%, chest tightness and shortness of breath will occur, and thoracentesis or closed chest drainage should be performed to restore the pressure in the chest cavity to negative pressure, so that the lung will reopen and the cardiopulmonary function will be normalized, and the respiratory function will become normal.