Pulmonary function test is to detect the volume, speed and pressure changes of the inhaled and exhaled gases in the human lungs through a pulmonary function test instrument to understand whether the respiratory function of the subject is normal. During the pulmonary function test, the patient only needs to follow the doctor’s instructions and breathe in the instrument in different ways according to the different test items to complete the entire test. Pulmonary function tests are relatively simple, quick and non-invasive, and are easily accepted by patients in clinical practice. Pulmonary function tests can detect early lesions in the upper and lower airways and lungs of patients, and can be used to identify the causes of dyspnea and assess the degree of damage to the physiological functions of the lungs from cardiopulmonary diseases. It is also used to assess the tolerance of thoracic and abdominal surgery, the assessment of cardiopulmonary tolerance in sports athletes and air/space pilots, and the determination of work capacity in sick and disabled patients. Respiratory diseases are common and frequent diseases in China. According to the statistics of the top ten major causes of death in some cities and rural areas in 2001, respiratory diseases (excluding lung cancer) accounted for the fourth cause of death in cities and the first cause in rural areas, ranking the first cause of death among the total population in China. With the accelerated urbanization, industrial economic development, urban air pollution, smoking and population aging, the incidence of respiratory diseases such as lung cancer and bronchial asthma has increased significantly in recent years, and the incidence of chronic obstructive pulmonary disease (COPD) remains high (more than 7% of people over 40 years old), so respiratory diseases pose a great danger to the health of our people. For chronic obstructive pulmonary disease (COPD), bronchial asthma and other chronic airway diseases, pulmonary function tests are especially important as an important basis for diagnosis and classification of the disease. Chronic obstructive pulmonary disease (COPD), also known as the “silent disease”, is caused by long-term smoking, air pollution and other factors that damage the airway, resulting in gradual impairment of lung function; its early symptoms are not obvious, and when shortness of breath appears, lung function is already severely impaired, so for these patients, lung function tests can be used to make a clear diagnosis at an early stage. Therefore, for these patients, pulmonary function tests can provide early diagnosis, prevention and treatment, thus slowing down disease progression. Pulmonary function tests include measurement of lung volume and ventilation function as well as diffusion function. For patients with bronchial asthma and chronic obstructive pulmonary disease, reversible airway obstruction and airway hyperresponsiveness should be measured during the pulmonary function test. NO is an indirect marker of chronic airway inflammation, which can help clinicians obtain more information about the severity of the disease, prognosis and the efficacy of anti-inflammatory drugs. The clinical application of pulmonary function tests in China is still unsatisfactory. According to the survey, only about 1/3 of the patients clinically diagnosed with chronic obstructive pulmonary disease have received pulmonary function tests, and the clinical application of pulmonary function tests in primary hospitals in China is almost in a blank state, and only 2.4% of patients in rural areas have received pulmonary function tests. Therefore, it is important to promote and carry out pulmonary function tests in clinical work. Today, as the public attaches more and more importance to health checkups, it is recommended that regular pulmonary function tests should be performed for the following groups of people: long-term smokers, people exposed to polluting gases/dust in the work environment, people with recurrent cough/coughing sputum, and people who feel chest tightness/shortness of breath after activity, especially if it gradually worsens. For patients with diagnosed respiratory diseases such as chronic obstructive pulmonary disease and asthma, regular lung function tests should be performed to assess the condition and help clinicians to formulate or adjust treatment plans in a timely manner.