Objective To evaluate the pulmonary function characteristics of patients with combined pulmonary fibrosis and emphysema (CPFE),and to examine whether distinguishing CPFE,emphysemaalone (EA),and pulmonary fibrosis (IPF) without emphysema by the pulmonary function method.Methods The pulmonary function parameters of 48 patients with CPFE,50 cases of EA,and 46 cases of IPF without emphysema were analyzed and compared by conventional methods of lung function testing and impulse oscillometry system.Results Total lung capacity (TLC)%0 pred was normal in CPFE group [(86.9±17.8) %].TLC%pred was decreased in IPF without emphysema group [(70.4±17.0)%].The forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) in CPFE group was normal [(72.0± 9.4)%].FEV1/FVC decreased in EA group [(56.5± 14.4)%].Diffusion capacity was lower in CPFEgroup [(57.2± 17.3)%],EA group [(62.8±25.7)%],and IPF without emphysema group [(66.9± 21.5)%],respectively.R5 % pred in CPFE group and IPF without emphysema group was normal by impulse oscillometry system.However,R5 % pred was significantly elevated in EA group [(161.3 ±69.0) %].R5-R20 increased in the three groups.Compared with CPFE group and IPF without emphysema group,R5 R20 increased significantly in EA group (P =0.006,P =0.013).In addition,X5 reduced in the three groups.Compared with CPFE group and IPF without emphysema group,X5 decreased significantly in EA group (P 0.004,P =0.047).In CPFE group and EA group,there was positive correlation between R5-R20 and RV/TLC (r =0.44,P =0.01; r =0.66,P =0.01).In CPFE group and EA group,there was negative correlation betweenX5 and RV/TLC (r =0.51,P =0.01; r =0.66,P =0.01).In IPF without emphysema group,there was correlation between TLC% pred and R5-R20 and X.5 (r =-0.50,P =0.01; r =0.6,P =0.01).Conclusions Pulmonary function features of CPFE show that lung volume,ventilation function,total airway resistance,and central airway resistance are normal,diffusion capacity and lung compliance are lower,peripheral airway resistance and elasticity resistance are higher. Key words: Pulmonary emphysema; Pulmonary fibrosis; Pulmonary function; Impulse oscillometry