The　ordering　behavior　and　the　mechanical　properties　of　the　doped　L1(2)　type　Al3Sc-based　intermetallics　were　studied　by　sublattice　model　supported　by　first-principles　calculations.　The　results　show　that　the　intermetallics　Al3Sc　is　a　fully　ordered　intermetallics,　where　Al　atoms　always　occupy　the　3c　sublattice　and　Sc　atoms　always　occupy　the　1a　sublattice.　L1(2)-A1(3)(Sc0.75M0.25)　intermetallics　(where　M=Y,　Ti,　Zr　and　Hf)　is　a　fully　ordered　intermetallics,　where　M　always　occupies　the　la　sublattice.　The　site　preference　of　these　alloying　elements　is　independent　of　the　heat　treatment　temperature.　L1(2)-Al-3(Sc0.75M0.25)　intermetallics　satisfy　the　mechanical　stability　conditions.　The　shear　modulus,　elastic　modulus,　Young＇s　modulus　and　the　hardness　of　L1(2)-Al-3　(Sc0.75M0.25)　intermetallics　are　smaller　than　those　of　L1(2)-Al3Sc.　While　the　shear　modulus,　elastic　modulus,　Young＇s　modulus　and　the　hardness　of　L1(2)-Al-3(Sc0.75M0.25)　intermetallics,　where　M=Ti,　Zr　or　Hf,　decrease　with　increasing　the　atomic　radius.　L1(2)-Al-3(Sc0.75Ti0.25)　has　the　best　plasticity　and　toughness　compared　with　other　L1(2)-Al-3(Sc0.75M0.25).