Background One-lung ventilation (OLV) is always applied during thoracic surgery. But OLV could cause severe inflammatory reaction, even worse the acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) which lead to really high mortality. Not only can the OLV harm the ventilated lung but also the hypoxia and the hypoperfusion could damage the collapsed lung. The injury of the collapsed lung may lead to severe inflammatory reaction even damage the distant organs, which will affect the prognosis and survival rate of the patients. Objective It is aimed to make a brief introduction of the possible mechanism which damaged the collapsed lung during OLV. Content The possible mechanism of the injury in the collapsed lung may focus on the following aspects: oxidative stress reaction, inflammatory reaction, decrease of the surface active substance and the collapsed lung edema. Trend It is for providing a theory evidence about how to prevent and treat the collapsed lung injury, by discussing its possible mechanism.