Eight　drivers　were　selected　with　ages　between　35　and　48.　Electrocardiograph,　Frecord　data　collecting　system　and　dynamics　GPS　were　utilized　to　study　the　drivers＇　behavior　on　braking　pedal　velocity　and　physiology　in　emergency.　The　mixing　effects　model　between　braking　pedal　velocity　and　physiology,　which　is　affected　by　obstacle　distance,　driving　velocity,　driving　time,　and　personality,　is　established　to　study　their　relationship.　The　results　indicate　that　the　distance　between　the　vehicle　and　obstacle　has　more　important　influence　on　the　greatest　braking　pedal　velocity　than　that　of　driving　speed.　The　study　provides　a　new　method　for　the　drivers＇　behavior　analysis　under　emergency.