Driver　fatigue　is　one　of　the　main　causes　of　traffic　accidents.　Many　researchers　believe　that　electroencephalography　is　very　accurate　and　promising　to　detect　driving　fatigue,　but　so　far,　the　research　results　have　been　variable.　Through　simulation　experiments,　this　paper　found　when　driving　at　night,　delta　band　varies　significantly　with　the　degree　of　fatigue.　The　results　have　implications　for　real-time　automatic　detecting　driver　fatigue　at　night　and　are　helpful　for　future　development　of　driver　fatigue　countermeasures.　©　2009　IEEE.