It　is　necessary　to　judge　the　emergency　degree　of　avoidance　for　traffic　safety.　Firstly　the　emergency　degree　is　given　based　on　the　augment　of　heart　rate　and　the　driving　proneness　is　introduced　to　tell　the　effect　of　driver＇s　basic　characteristic　by　the　augment　of　heart　rate.　Then　the　control　algorithm　of　vehicle　motion　under　emergency　is　established　and　simulated　with　Simulink.　The　results　show　that　the　drivers＇　characteristics　have　obvious　effects;　the　bigger　emergency　degree　is,　the　greater　maximum　deceleration　is　used,　which　is　about　-5　-　-6　m/s2,　the　time　is　about　5　-　7　s.　The　study　is　helpful　to　understand　the　driver＇s　behavior　under　emergency　and　to　provide　basis　for　the　driver　safety　management.