Abstract： Objective To observe the effects of positive end-expiratory pressure(PEEP) on oxygen utiliza-tion coefficient in patients with acute respiratory distress syndrome(ARDS). Methods 28 ARDS patients with me-chanical ventilation were studied. Catheter of central vein was laid. Increment levels of PEEP(0,5, 10, 15 and 20cmH2O) were applied sequentially. Hemodynamics and oxygen metabolism parameters were measured and calcula-tion of O2 UC [O2 UC = (SaO2 -SvO2.)/SaO2] were carried out respectively. O2 UC in 30 normal subject groups were carried out. Results Arterial oxygen tension(PaO2) increased significantly(P < 0.05) at PEEP 5cmH2O. Oxygen u-tilization coefficient (O2 UC), heart rate(HR) and mean blood pressure (MBP) were not significantly different (P >0.05) at PEEP 10cmH2O. At PEEP 15cmH2 O, O2UC and HR increased significantly (P < 0.05), but M BP reduced obviously(P < 0.05). Conclusions Too high PEEP can result in oxygen utilization coefficient of ARDS patient de-acend furthur, can not really correct oxygen difieiency condition in patients' organization cell. The optimal PEEP should be found, and blood capacity should be appropriately increased.