By　means　of　the　computational　fluid　dynamics　software　Fluent　6.　3,　a　mathematical　model　of　three-dimensional　three-phase　fluid　flow　field　in　the　molten　bath　of　electric　arc　furnace　(EAF)　with　side　accessorial　oxygen　lances　was　developed　to　study　the　transient　phenomena　of　oxygen　jet　impingement　on　the　molten　steel　and　the　molten　slag.　The　water　modeling　experiment　was　carried　out　to　verify　the　simulation　results.　The　impingement　of　the　supersonic　oxygen　jet　caused　impact　dent　on　the　molten　steel　surface　accordingly.　The　area　of　impact　dent　changed　almost　in　linear　relationship　to　flow　rate　of　oxygen　jet,　which　can　be　expressed　by　a　deduced　mathematical　equation.　And　the　relationship　between　the　impact　force　of　oxygen　jet　and　the　correspondingly　formed　apparent　static　pressure　on　molten　bath　was　obtained,　which　was　in　linear　relationship　and　a　direct　proportion,　and　can　also　be　expressed　by　a　deduced　mathematical　equation.