The study demonstrates that diazepam could significantly prolong the survive time in normobaric, hypobarie and NaNO_2 hypoxia.This effect is prominent even at low dosage (2mg/kg).compared with pentobarbital,the diazepam is superior in the protection of cerebral anoxia,with a higher curative effect,less toxicity and side effect.The effect of diazepam against normobaric hypoxia is abolished by picrotoxin.The possible mechanism of diazepam against hypoxia is also discussed.