Based　on　the　survey　data　of　six　signalized　intersections　with　dual　left-turn　lanes　in　Beijing,　the　saturation　time-headways,　saturation　flow　rates　and　their　influencing　factors　of　dual　left-turn　lanes　at　signalized　intersections　were　studied　by　using　statistical　methods.　By　comparing　with　arithmetic　mean　value　and　median　value,　the　trimmed　mean　value　method　was　used　to　calculate　the　saturation　time-headway　and　saturation　flow　rate.　The　effects　of　lane　width　and　turning　radius　on　the　saturation　flow　rate　were　studied,　and　the　regression　model　of　saturation　flow　rate　with　turning　radius　was　suggested.　The　saturation　flow　rates　of　inside　lane,　outside　lane　and　single　left-turn　lane　were　compared.　Analysis　result　shows　that　the　saturation　time-headway　of　inside　lane　is　2.14~2.60　s,　the　saturation　time-headway　of　outside　lane　is　2.08~2.37　s,　and　the　average　saturation　flow　rate　is　1600　pcu　·　(h　·　lane)-1.　The　ratio　of　sum　saturation　flow　rate　of　inside　lane　and　outside　lane　to　that　of　single　left-turn　lane　is　1.80~2.05.