Objective To observe the changes of brain oxygenation in patients with extremely severe craniocerebral injury and the therapeutic effect of early normobaric hyperoxia.Methods Sixtyeight patients with extremely severe craniocerebral injury treated from January 2011 to January 2013 were assigned to two groups according to the random number table:50％ oxygen breathing for one week in control group (34 cases) and 80％ oxygen breathing for one week in treatment group (34 cases).Blood samples from jugular vein and radial artery were collected at 1,3,5,and 7 days to measure indices of blood gas analysis,i.e.,PaO2,PjvO2,CaO2,CjvO2,Da-jvO2,CERO2 and Djv-a Lac.GCS and content of neuron-specific enolase (NSE) were recorded as well.Results Values of PaO2 at each time point and GCS at 5 and 7 days were significantly higher in treatment group than in control group (P ＜0.05).Djv-a Lac at 3,5 and 7 days and NSE at 7 days revealed significantly higher levels in treatment group than in control group(P ＜ 0.05).Whereas at each time point,there were no significant differences between the two groups in aspects of PjvO2,CaO2,CjvO2,Da-jvO2 and CERO2 (P ＞ 0.05).Conclusion Early use of 100％ oxygen in patients with extremely severe craniocerebral injury may be beneficial to the prognosis.