During this study, we provided small VT (6～8mL/kg )through maintaining the PI≤30cmH₂O (1cmH₂O=0.098 kPa) by PCV to assess the effects of sighs on hemodynamics. Twenty patients with ALI admitted from november 2006to November 2008in intensive care unit of Hebei General Hospital were enrolled in the study. Observation indicates that persistent sighs significantly improve oxygenation and compliance of respiratory system of ALI patients. The treatment proves to be safe and simple, having little interference to hemodynamics.