The alveolar arterial partial pressure difference, which refers to the difference between the alveolar partial pressure and the arterial partial pressure, is an important basis for determining whether pulmonary ventilation is normal or not. In the resuscitation of CPR patients, the alveolar arterial partial pressure difference is an important indicator of the patient’s prognosis after resuscitation, and can be measured by arterial blood sampling and blood gas analyzer. Its decrease indicates plateau hypoxemia, while an increase can be seen in pulmonary asplenia and adult respiratory distress syndrome. A moderate increase can be seen in acute exacerbations of chronic obstructive pulmonary disease and chronic bronchitis. Mild increases may be caused by alveolar hypoventilation and are seen in asthma, pneumonia, etc. The examination can be followed by relevant treatment for the cause.