Spontaneous pneumothorax can be divided into primary pneumothorax and secondary pneumothorax according to the presence or absence of combined pulmonary disorders before the occurrence of pneumothorax. Traumatic pneumothorax is a pneumothorax caused by chest trauma or during medical diagnosis and treatment operations. Artificial pneumothorax is the artificial injection of gas into the pleural cavity for the diagnosis and treatment of intrathoracic diseases. According to the relationship between pneumothorax and external air, it can be divided into: ① closed pneumothorax: the pleural fissure is small, closed with lung atrophy and plasma exudation, no more air leaks into the pleural cavity, the intrathoracic pressure is close to or exceeds the atmospheric pressure, and the intrathoracic pressure drops after pumping; ② open pneumothorax: the pleural fissure is continuously open, the gas goes in and out of the pleural cavity freely with breathing, the intrathoracic pressure fluctuates above and below the atmospheric pressure, and the pressure does not change after pumping; ③ Tension pneumothorax: the pleural fissure is a one-way valve or piston, the fissure opens when inhaling, air enters the pleural cavity; when exhaling, the fissure closes, gas cannot be discharged, resulting in the accumulation of more and more air in the pleural cavity, the intrathoracic pressure rises rapidly to positive pressure, and then becomes positive shortly after pumping to negative pressure. This kind of pneumothorax causes the greatest pathophysiological changes, and can lead to sudden death if not treated in time to decompress. In addition, there are some special pneumothoraxes, such as menstrual pneumothorax, pregnancy combined pneumothorax and elderly spontaneous pneumothorax. Under normal circumstances, there is no gas in the pleural cavity because the sum of various gas partial pressures in capillary blood is only 706 mmHg, which is 54 mmHg lower than the atmospheric pressure. the negative pressure in the chest cavity during the respiratory cycle is caused by the outward expansion of the thorax and the inward elastic retraction of the lungs. The presence of gas in the thoracic cavity occurs only under three conditions: ① a breach between the alveoli and the thoracic cavity, where gas will enter the thoracic cavity from the alveoli until the pressure difference disappears or the breach closes; ② trauma to the chest wall producing traffic with the thoracic cavity; ③ the presence of gas-producing microorganisms in the thoracic cavity. Clinically, it is mainly seen in the first two cases. Spontaneous pneumothorax is one of the most common emergencies in internal medicine. Primary pneumothorax occurs in healthy individuals without definite underlying lung disease, but rupture of subpleural pulmonary blisters may be the primary mechanism of pneumothorax, and smoking is one of the etiologies of pulmonary blister development in healthy individuals. Secondary pneumothorax occurs in patients with underlying pulmonary disease.