Lung function in chronic bronchitis can be normal in the early stages, but is abnormal when the disease progresses and leads to chronic obstructive pulmonary disease. Lung function can be normal in the early stages of chronic bronchitis, and some patients may have small airway obstruction. When chronic obstructive pulmonary disease develops, it is characterized by abnormal lung function, with lung function results suggesting that the ratio of force expiratory volume in the first second (FEV₁) to forceful lung volume (FVC) is reduced and less than 70% after inhalation of bronchodilators, and that residual airflow is increased. Patients with chronic bronchitis undergo pulmonary function tests, and if the FEV₁/FVC is <70% after inhalation of bronchodilators, it is necessary to consider that chronic bronchitis may have progressed to COPD, and that bronchodilators such as tiotropium bromide can be used for long-term control of the disease. Patients with chronic bronchitis should go to the hospital in a timely manner to improve the relevant examinations under the guidance of specialists and to develop a treatment suitable for individual conditions.