The　3003　aluminum　alloys　with　four　different　initial　grain　sizes　were　deformed　by　isothermal　compression　in　the　range　of　deformation　temperature　300-500　A　degrees　C　at　strain　rate　0.01-10.0　s(-1)　with　Gleeble-1500　thermal　simulator.　The　results　show　that　the　smaller　the　initial　grain　size　of　the　alloy,　the　greater　the　required　deformation　resistance,　and　the　smaller　the　peak　strain,　which　is　conducive　to　the　occurrence　of　dynamic　recrystallization　(DRX).　The　DRX　critical　strain　increases　with　the　decrease　of　the　deformation　temperature　or　the　increase　of　the　strain　rate,　and　the　DRX　volume　fraction　increases　with　the　decrease　of　the　strain　rate　and　the　increase　of　the　deformation　temperature.　The　average　grain　size　of　3003　aluminum　alloy　after　deformation　is　smaller　than　that　before　deformation.　The　smaller　the　initial　grain　size,　the　lower　the　critical　recrystallization　strain.　So　the　DRX　is　carried　out　more　fully,　contributing　to　the　thermoplastic　deformation　of　the　alloy.