The pleural cavity is a closed potential cavity formed by the two layers of the dirty wall of the pleura turning and moving at the root of the lung, consisting of the dirty layer of the pleura immediately on the surface of the lung and the wall layer of the pleura immediately on the inner wall of the thorax, one on each side, not connected to each other, no gas in the cavity, only a small amount of plasma, which can reduce the friction during breathing, when normal, no pleural friction sounds can be heard. The negative pressure inside the cavity is conducive to the expansion of the lung and the return of venous blood and lymphatic fluid. The pleura is a plasma membrane structure, which is laid on the inner surface of the thorax and outside the thoracic organs, with a cavity in the middle, where the negative pressure can increase or decrease with respiratory movement. The lower outer corner of the pleural cavity is called the costo-diaphragmatic sinus, also known as the costo-diaphragmatic angle, which is the lowest position and is the first place where fluid accumulates in the pleural cavity, so it can be used more often for puncture; the heart and diaphragm intersect to form the cardio-diaphragmatic sinus or cardio-diaphragmatic angle, which is deformed when the heart is diseased; there is pleura between the lung lobes, and fluid can also accumulate in the interlobular pleura in certain exudative inflammation; the apical pleural cavity is located 2-3 cm above the clavicle, which is the first place filled with gas when the pleural cavity accumulates, so it has diagnostic significance in It has diagnostic significance clinically. The presence of gas in the pleural cavity occurs only in three cases: 1) a breach between the alveoli and the pleural cavity, where gas will enter the pleural cavity from the alveoli until the pressure difference disappears or the breach closes; 2) trauma to the chest wall producing traffic to the pleural cavity; 3) the presence of gas-producing microorganisms in the pleural cavity. Clinically, the first two conditions are mainly seen. Spontaneous pneumothorax is one of the most common medical emergencies, with an annual incidence of 18-28/100,000 in healthy adult males and 1.2-6/100,000 in females.