Objective To investigate the lung function testing performing in normal smokers,and urge smokers to stop smoking early. Methods Two hundred and one adult men did the pulmonary function testing by MINATO AS-505 portable spirometer, and analyzed the effect d different smoking degree on the pulmonary function. Results There was no relationship between lung volume index and smoking, smoking degree. Compared with nonsmokers, the indicants such as FEV1, MVV, FEV1/FVC had decreased, and the indexes of the small airway function (PEF, FEF25%-75%)had significantly dropped in the smokers. And the smokers especially long-term smokers, most indexes of the pulmonary functions and all indexes of the small airway function correlated with smoking index. Conclusion Although smokers do not show clinical symptoms, their lung functions have been reduced, especially small airway function.