Pulmonary function test is one of the important examination methods in respiratory medicine, which plays a key role in the diagnosis, severity grading, treatment and prognosis evaluation of respiratory system diseases. Pulmonary function tests mainly include two parts: ventilation function and ventilation function tests. Clinically, ventilation dysfunction is the most common and is divided into obstructive, restrictive and mixed ventilation dysfunction, and this criterion has been used for many years and is widely accepted. However, the debate on determining the nature and severity of ventilatory dysfunction has not stopped. Currently, the diagnosis of obstructive ventilatory dysfunction mainly relies on FEV1/FVC, but it has problems such as poor early diagnostic sensitivity and difficulty in completion in elderly or more severely ill patients; FEV1 % of expected value is mainly used to determine the severity of obstructive ventilatory dysfunction, but in patients with mixed ventilatory dysfunction, because the reduction of FEV1 is affected by both obstruction and restriction FEV1 as % of predicted value is difficult to accurately evaluate the degree of obstruction. Therefore, in recent years, many scholars have investigated indicators such as FEV3, FEV6 and corrected FEV1, hoping to remedy the deficiencies of FEV1/FVC and FEV1 as % of predicted value.