The　effects　of　addition　of　Er　and　Zr　on　the　aging　precipitation　phase　and　mechanical　properties　in　cast　Al-Cu-Mn-Si-Mg　alloy　were　studied.　The　addition　of　Er　and　Zr　can　refine　the　as-cast　grains.　The　average　grain　size　of　as-cast　alloy　containing　Er　and　Zr　is　140.60　mu　m,　while　the　average　grain　size　of　as-cast　alloy　without　Er　and　Zr　is　168.54　mu　m.　After　T6　heat　treatment,　the　yield　strength　of　the　alloy　containing　Er　and　Zr　reached　334.3　MPa,　while　the　yield　strength　of　the　alloy　without　Er　and　Zr　was　only　284.3　MPa.　After　aging　the　strengthening　precipitates　of　both　alloys　contain　theta　＇　phase,　Q　＇　phase　and　T　phase.　In　the　alloys　containing　Er　and　Zr　the　Al3(Er,　Zr)　phase　with　L12　structure　precipitated　during　the　solution　process,　which　reduced　the　diameter　of　the　theta　＇　phase　during　subsequent　aging.　After　T6　heat　treatment,　the　precipitation　strengthening　contributed　67.09　%　and　61.31　%　to　the　total　strength　of　the　alloy　with　Er,　Zr　and　without　Er,　Zr,　respectively.