【Abstract】 Objective To investigate the evaluation value of oxygenation index and prognosis in patients with acute respiratory distress syndrome (ARDS) at different time points.Methods 89 ARDS diagnosed from March 2015 to November 2017 were selected and retrospectively analyzed. All patients received the mechanical ventilation (MV), and then were divided into survival group (47 cases) and death group (42 cases) according to 28d prognosis. The survival group was further divided into two subgroups, namely, highlevel oxygenation index group (n=22, oxygenation index ≥150mmHg, 1mmHg=0133kPa) and lowlevel oxygenation index group (n=25, oxygenation index＜150mmHg), according to oxygenation index at different time points of MV. The oxygenation index was calculated at MV immediately, after recruitment maneuver (RM) and at 6, 12, 24 hours of MV, moreover, the vital signs ［heart rate (HR), systolic blood pressure (SBP), respiratory rate (RR), arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2)］, and ventilator related parameters ［positive endexpiratory pressure (PEEP), minute ventilation (VE), tidal volume (VT), and pulmonary dynamic compliance (Cdyn)］were measured at MV immediately and 24 hours of MV. Then the predictive value of oxygenation index at different time points for the 28d prognosis of ARDS was analyzed. Results The oxygenation index of the two groups after RM, MV6h, MV12h and MV24h was significantly higher than that of MV0h (P＜005), no difference was found at the MV0h (P＞005). The oxygenation index of survival group was significantly higher than that of death group after RM, MV6h, MV12h and MV24h (P＜005), no difference was found at the MV0h (P＞005). The low level oxygenation index group was significantly higher than the high level oxygenation index group at MV6h, MV12h and MV24h (P＜005). The PEEP, VT and VE levels of death group was significantly higher than the survival group at MV 24 h, while Cdyn was significantly lower than the survival group (P＜005). Taking the oxygenation index after RM as prognostic index, the AUC was 0670; oxygenation index at MV 6h, 12h and 24 h had higher prognostic value for ARDS patients, AUC were 0732, 0746, 0762, respectively, while no difference was found in oxygenation index at MV5h, MV12h, MV24h. Conclusion The oxygenation index of patients with ARDS after early pulmonary retraction can be used as the main index to evaluate the prognosis of patients, furthermore, the oxygenation index after MV is the key time point for predicting the 28d prognosis, which is worthy of promotion.