Driving　fatigue　is　one　of　the　main　causes　for　fatal　accidents.　Environmental　stimulus　as　the　countermeasure　against　driving　fatigue　has　been　widely　researched.　For　this　paper　a　driving　simulator　experiment　was　carried　out　in　order　to　validate　the　effect　of　sound　as　the　environmental　stimulus　countermeasure.　Firstly,　the　paper　analyzed　the　change　law　of　ECG　(Electrocardiograph)　with　driving　time,　then　validated　that　it　was　reasonable　to　consider　ECG　as　an　evaluation　indicator　of　driving　fatigue.　Various　indices　of　ECG　recorded　from　alert　to　fatigue　throughout　the　experiment　were　used　to　measure　degree　of　fatigue　using　principal　component　analysis　(PCA).　Finally,　being　a　countermeasure　against　driving　fatigue,　the　validity　of　sound　stimulus　was　verified　and　the　optimal　combination　of　sound　was　presented　by　orthogonal　experiments.　The　results　show　that　the　alerting　reaction　exists　in　the　sound　signal　stimulation　during　driving　fatigue　state,　and　there　is　a　significant　difference　among　different　types　of　sound　stimulus.　Stimulating　interval　and　sonic　intensity　are　the　most　significant　factors　to　fight　driving　fatigue,　the　impact　of　frequency　and　stimulating　interval　are　weaker.　The　experimental　method　will　lay　a　foundation　for　further　study　on　light　and　vibration　stimulus　as　countermeasures　against　driving　fatigue.　©　2010　ASCE.