Objective To explore the effect of positive end expiratory pressure (PEEP) on arterial oxygenation and intrapulmonary shunt during one-lung ventilation (OLV) and pulmonary function during perioperation. Methods Forty patients with normal pulmonary function,ASA I - II :scheduled for pulmonary lobectomy, were divided into control group and PEEP group by random digits table with 20 cases each. Patients were induced by double-lumen tubes under intravenous anesthesia and were received 10 ml/kg tidal volume, 12 frequents/min breathing rate during the two-lung ventilation (TLV), secondary reduced to 6 ml/kg tidal volume, 16-18 frequents/min breathing rate without PEEP (control group) or with 5 cm H2O cm H2O =0.098 kPa) PEEP (PEEP group) during OLV.Hemodynamics and respiratory mechanical parameters were continuously monitored, lung function before operation and at 72 h after operation was detected. Results Compared to before OLV,arterial oxygen tension (PaO2), arterial oxygen saturation (SpO2), oxygenation index (OI) were decreased and intrapulmonary shunt ratio (Qs/Qt) was increased in control group and PEEP group at 30 min after OLV (P < 0.01 or < 0.05). However,PaO2 and SpO2 and OI were higher and Qs/Qt was lower in PEEP group than that in control group at the same time point (P<0.05). In addition, FEV1%, FVC% and FEV1/FVC were (121.8 ± 25.0% ,(117.2 ± 24.3)% , (87.6 ± 15.7)%before operation and (84.9 ± 21.6)%, (77.2 ± 18.3)% , (70.5 ± 12.5)% at 72 h after operation respectively in control group, (116.9 ±24.5)% , (112.1 ±23.6)% , (85.3 ± 13.8)% before operation and (96.3 ± 20.4)%, (88.1 ± 19.8)% , (78.4 ± 10.2)% at 72 h after operation respectively in PEEP group. Although decreased in control group and PEEP group at 72 h after operation comparing with preoperation (P< 0.01 or < 0.05 ), FEV1%, FVC% and FEV1/FVC were higher in PEEP group than those in control group at 72 h after operation (P<0.05). Conclusion Appropriate PEEP increases arterial oxygenation,reduces Qs/Qt and improves pulmonary function during OLV,reduces the risk of hypoxernia and lung injury induced by OLV during perioperation.