Normal lung function does not confirm the diagnosis of chronic obstructive pulmonary disease; normal lung function can rule out the possibility of chronic obstructive pulmonary disease. Chronic Obstructive Pulmonary Disease (COPD) is a chronic inflammatory disease of the airways characterized by restricted airflow and incomplete reversibility. Caused by a variety of reasons, the most common are chronic bronchitis and emphysema, due to the existence of respiratory airflow limitation, and incomplete reversibility, so the pulmonary function test of chronic obstructive pulmonary disease can not be normal, the performance of obstructive ventilation dysfunction, and the first second expiratory volume of exertion of the expiratory volume percentage, to measure and judge the existence of respiratory airflow limitation, in order to be less than 70% of the expected value of the standard. Criteria. If the percentage of expiratory volume in the first second as a percentage of expiratory volume with exertion is greater than 70% of the predicted value, chronic obstructive pulmonary disease can be excluded.