Abstract： Objective:To investigate the prevalence of abnormal lung ventilation function in asymptomatic subjects receiving healthy examination and the risk factors of small airway dysfunction (SAD).Methods:From August 2016 to October 2017, the pulmonary function test results of 610 healthy subjects who met the standards of this study in Fuxing Hospital affiliated to Capital Medical University were analyzed. The detection rate of abnormal lung function was described; the difference of lung function was compared between smokers and non-smokers, among groups with different smoking age, between individuals with normal body mass index and obese individuals; the risk factors of SAD was investigated; and the characteristics of abnormal lung function in asymptomatic subjects receiving physical examinations were summarized.Results:Among the 610 subjects, the overall prevalence of abnormal pulmonary function was 42.6%, and the rate of obstructive, restrictive, mixed and pure SAD were 16.7% and 5.9%, 2.5% and 17.5% respectively. The prevalence of the ratio of forced expiratory volume in 1 second (FEV 1) to forced vital capacity (FVC) (FEV 1/FVC) less than 70% was 4.6%; small airway function indicators of maximal mid expiratory flow (MMEF), forced expiratory flow at 50% and 75% of forced vital capacity (FEF 50% and FEF 75%) for smokers were significantly lower than that of non-smokers, and decreased progressively with smoking age. Smoking was an independent risk factor for SAD. Compared with non-smokers, smokers had a 65-fold increase in the risk of SAD. Obesity was not associated with SAD. Conclusions:The prevalence of abnormal lung function is high in asymptomatic subjects receiving healthy examination. The main abnormalities are obstructive ventilation dysfunction and SAD. Cigarette smoking is the major risk factor for SAD.