To probe into the mechanism of pneumothorax caused by acupuncture or acupoint injection and the preventive methods.Retrospectively analyze the clinical original symptoms of 38 cases with pneumothorax caused by acupuncture and acupoint injection, which were divided into four clinical types: dyspnea type, shock type, thoracalgia type and tardy type. Illustrate the relation of the clinical types with severe degrees of pneumothorax, and the mechanism of pneumothorax inducing death of the patient.In the series there were 38 cases with pneumothorax induced by acupuncture or acupoint injection, including 4 cases of dyspnea type, 16 cases of shock type, 14 cases of thoracalgia type, 4 cases of tardy type. After proper treatment, 37 cases were cured and one case of dyspnea type died of tension pneumothorax.The mechanism of pneumothorax caused by acupuncture or acupoint injection is that due to the filiform needle tip or the syringe's needle tip inserting into the lung tissue at the patient's respiration in acupuncture or acupoint injection, the filiform needle tip or the syringe's needle tip lacerates the lung tissue. Air in alveolus goes into the thorax pleura cavity to form pneumothorax. In acupuncture or acupoint injection, the needle tip must not insert into the lung tissue, which is a key for prevention of pneumothorax.