Ｏｂｊｅｃｔｉｖｅ　To observe the effect of different level of positive end expiratory pressure (PEEP) on the lung compliance and oxygenation of the patients undergoing laparoscopic surgery with head down position, and to investigate the appropriate level of PEEP in those surgery.　Methods　Forty-five ASAⅠ or Ⅱpatients undergoing elective laparoscopic rectum and colon surgery were included in this study. Patients were divided into 3 groups by a random number method(n=15): PEEP=0 (group Ⅰ), PEEP=4 cmH2O(1 cmH2O=0.098 kPa, group Ⅱ), PEEP=8 cmH2O (group Ⅲ). Volume control ventilation mode was set to maintain the PETCO2 between 35 mmHg and 45 mmHg(1 mmHg=0.133 kPa). The PETCO2 and lung dynamic compliance (Cdyn) was recorded in five time points: after the induction of anesthesia (T0), 10 min after the beginning of the operation (T1), 30 min (T2) and 60 min(T3) after the implementation of different levels of PEEP, 10 min before the end of surgery(T4). Blood samples were also obtained from radial artery and right internal jugular vein at the same time to calculation the dead space ventilation ratio(Vd/Vt) and intrapulmonary shunt(Qs/Qt).　Results　Demographic profile, HR and MAP were similar in these three groups(P>0.05). The Cdyn of all three groups released at T1 to T0 (P<0.05). The Cdyn of group Ⅱand group Ⅲ increased at T2, and both of them at T4 [groupⅡ(50.9±9.8) ml/cmH2O, group Ⅲ(58.8±13.4) ml/cmH2O] were still higher than at T0[groupⅡ(47.6±10.6) ml/cmH2O, group Ⅲ(51.3±10.8) ml/cmH2O](P<0.05), the Cdyn of group Ⅲ was entirely higher than group Ⅰ at T2 and T3[T2, group Ⅲ (42.8±9.9) ml/cmH2O, groupⅠ(29.3±8.0) ml/cmH2O, T3, group Ⅲ (42.9±10.3) ml/cmH2O, groupⅠ(29.3±8.6) ml/cmH2O](P<0.05). The Vd/Vt of all three groups increased at T1 (P<0.05). Among them, the Vd/Vt of both groupⅠand group Ⅲ at T4 [groupⅠ(21.5±7.6)%, group Ⅲ(24.2±6.8)%] were higher than at T0[groupⅠ(9.5±5.8)%, group Ⅲ(10.7±5.2)%](P<0.05), while the Vd/Vt of group Ⅱ at T4 was comparable to T0[T4(12.2±6.8)%, T0(9.9±7.8)%](P>0.05), and at the same time was significantly smaller than the value of group Ⅰ and group Ⅲ (P<0.05). The Qs/Qt of group Ⅱ at T4 was lower than groupⅠ[groupⅡ(12.3±6.3)%, groupⅠ(26.2±20.8)%] (P<0.05). Central venous partial pressure of oxygen(PvO2) of all three groups were gradually increased (P<0.05). First and foremost both the PaO2 and PvO2 of group Ⅱ at T4 were higher than the other two groups (P<0.05).　Conclusions　The lung compliance and oxygenation of the patients undergoing laparoscopic surgery with head down position can benefit from the implementation of positive end expiratory pressure. Implementing the PEEP of 4 cmH2O in this study can not only improve the lung compliance and oxygenation, but also reduce the dead space ventilation ratio and the intrapulmonary shunt.