FEV1 is the ratio of the measured FEV1 to the calculated FEV1, and is an important index used to evaluate respiratory function during pulmonary function tests. In clinical practice, the FEV1 test percentage can be used in the clinical evaluation of patients with chronic obstructive pulmonary disease, asthma and interstitial lung disease. The normal range of the specific index should be greater than 80% of the expected value, and if there is a significant decrease in FEV1, it indicates that the patient’s ventilatory function is abnormal. The analysis and judgment should be made in conjunction with the overall status of the patient.