The significance of pulmonary function test includes: 1, discovering abnormal pulmonary function: such as the early detection of slow-onset lung after the examination of frequent smokers; 2, diagnosing some diseases: including unexplained cough, the cause of which can be identified through the examination; some unexplained dyspnea, the cause of which can be found after the pulmonary function test, such as asthma and slow-onset lung; interstitial lung diseases, which can be diagnosed through this test, can be diagnosed in a timely manner; 3, preoperative assessment examination: to determine whether the patient can tolerate the surgery, which is helpful for preoperative screening.