Abstract： Objective:To investigate the characteristics of lung function impairment and its influencing factors in smoking men with non-chronic obstructive pulmonary disease (COPD).Methods:A total of 230 non-COPD men who attended the smoking cessation clinic of the Second Affiliated Hospital of Chongqing Medical University from October 2021 to August 2022 were prospectively assessed. Participants were categorized into three age groups:<40 years old group (65 cases), including smokers (53 cases) and non-smokers (12 cases); 40-60 years old group (109 cases), including smokers (73 cases) and non-smokers (36 cases);>60 years old group (56 cases), including smokers (20 cases) and non-smokers (36 cases). In this study, we compared the lung function indices of male smokers and non-smokers in different age groups , analyzed the possible factors affecting the lung function of smokers by linear regression , and compared the changes in the lung function of male smokers before and after smoking cessation. Results:In the<40 years old group, smokers′ forced vital capacity ratio (FVC)% predicted value (%pred), maximal mid expiratory flow (MMEF)%pred, forced expiratory flow after 75%/50% of the FVC has been exhaled (FEF 75, FEF 50)%pred, diffusing capacity of the lungs for carbon monoxide (DLCO)%pred, and the ratio of DLCO to alveolar volume (DLCO/VA)%pred were all lower than non-smokers (all P<0.05). Similarly, in the 40-60 years old and>60 years old groups, compared with non-smokers, forced expiratory volume in one second (FEV 1)%pred was significantly lower in smokers than in non-smokers ( P<0.05). FEV 1%pred ( β=-0.728, 95% CI:-0.026, 0.011), FVC%pred ( β=-0.332, 95% CI:-0.012, 0.003), FEF 50%pred ( β=-0.455, 95% CI:-0.03, -0.007), residual volume (RV)%pred ( β=0.371, 95% CI: 0.008, 0.041), RV to total lung capacity ratio (RV/TLC)%pred ( β=0.454, 95% CI: 0.011, 0.035) and MMEF%pred ( β=-0.324, 95% CI:-0.022, -0.002) were all influenced by the smoking index. All small airway function indices improved after smoking cessation (all P<0.05). Conclusion:Impairment of lung function in male smokers with non-COPD is characterized by early impairment of lung volume, lung diffusion function and small airway function, which progresses to impairment of lung flow rate with age, as influenced by smoking index and age.