Animal experimentals have shown that the more physiology-driven airway pressure release ventilation (APRV) methodologies in ARDS may significantly improve alveolar recruitment and gas exchange, increased homogeneity, and attenuate lung injury, without circulatory depression, as compared with conventional low tial volume lung protective ventilation. our previous single centre,random control study showed that clinical benefit for early use of APRV in ARDS. Nonetheless, clinical data on ARDS are still limited, most of them derived from small clinical trials in which variable outdated APRV settings were used, consequently, the findings of these studies were controversial. Additionally, the previous single-centre,random control study showed that clinical benefit for APRV.Therefore,the investigators are ready to design a multiple centres,random control study to further verify the effect of APRV plus protocol in ARDS.