Past　studies　indicate　that　traffic　accident　increases　in　bad　weathers　remarkably.　In　order　to　study　the　effects　of　bad　weathers　on　drivers,　this　paper　records　the　physiological　and　psychological　reactions　of　the　drivers　in　different　weathers　as　fine,　medium　rain,　heavy　rain,　rain　and　fog　based　on　driving　simulator.　Through　comparison　of　heart　rate,　breath　rate　of　the　drivers　and　the　speed　of　the　vehicles　between　different　weathers,　driver　behaves　in　different　weathers　are　obtained.　Experiments　indicate　that　the　speed　of　the　vehicle　varies　in　different　weathers.　The　speed　in　fine　is　the　most,　and　the　following　is　that　in　medium　rain,　heavy　rain,　rain　and　fog.　The　physiological　and　psychological　reactions　vary　in　different　weathers　too.　The　mean　heart　rate　in　medium　rain　is　the　most,　and　the　following　is　that　in　fine,　heavy　rain,　rain　and　fog　in　turn.　The　standard　deviation　of　the　heart　rate　in　medium　is　the　biggest,　and　the　following　is　that　in　rain　and　fog,　heavy　rain　and　fine.　The　paper　analyses　the　factors　affecting　the　driver　behaves　and　draws　the　conclusions　that　the　mean　speed　in　different　weathers　correlates　with　visibility　closely　and　that　the　heart　rate　correlates　with　the　driver＇s　tension　and　speed.　The　conclusions　provide　an　basic　data　for　posted　speed　limit　in　bad　weathers.