Expiratory index is a general term for many indicators commonly used in pulmonary function tests, including the following. The normal value of tidal volume is 0.5 liters, the normal value of compensatory respiratory volume is 1.68 liters, the residual air volume is at 1.55 liters, the average value of spirometry is around 4.13 liters depending on the population, the total lung volume is generally at 5.67 liters, the normal value of expiratory frequency in the lung ventilation index is around 14 times per minute, the alveolar ventilation volume is around 4 liters, the ventilation volume per minute is around 6 liters, the maximum autonomous minute ventilation volume is around 150 liters, ventilation reserve is generally greater than or equal to 93%, and the normal value of force spirometry is at 4.13 liters. In conclusion, expiratory indices need to be analyzed separately according to different testing indicators to further assess the patient’s lung function status.