By　Fluent　6.3,　develop　a　mathematical　model　of　three-dimensional　and　three-phase　flow　in　the　molten　bath　of　EAF　with　side　accessorial　oxygen　lance　to　study　the　transient　phenomena　of　jet　impingement　on　the　molten　steel　and　the　molten　slag.　The　simulation　result　shows,　the　impingement　of　the　supersonic　oxygen　jet　will　cause　flow　of　molten　steel　and　the　molten　slag　by　inspiring　wave　of　the　molten　bath　surface　from　the　impinged　hollow　centre　to　the　bath　centre,　and　will　cause　vortexes　under　bath　which　become　the　centre　of　molten　steel　circumfluence.　The　velocity　of　flowing　molten　steel　under　the　oxygen　lance　or　around　furnace　wall　will　be　faster　than　that　at　the　center　of　bath.　With　oxygen　jet　enhance,　the　frequency　of　the　molten　bath　surface　wave　will　increase,　and　the　center　of　vortexes　will　be　more　apart　from　the　impingement　point　of　jet　and　will　be　lower　to　the　bottom　of　bath,　the　number　of　vortexes　will　increase　and　the　effect　of　impingement　on　molten　steel　will　increase　accordingly.