The　site　occupancy　ordering　behaviours　of　the　alloying　elementi　in　Ti-Al　intermetallic　compounds　are　of　fundamental　and　technical　importance.　Based　on　the　crystallographic　information　of　Ti3Al　and　Ti2AlNb-　based　intermetallics　,　the　two-sublattice　model　and　three-sublattice　model　were　established　,　respectively.　The　quantitative　relationship　among　the　site　occupying　fraction　of　the　constituent　elements　vs.　alloy　composition　and　temperature　were　studied　theoretically　without　referring　experimental　data　as　input.　The　predicted　results　show　that　for　the　ternary　alloying　element　in　D019-type　Ti3A-based　alloys　,Ga　and　Sn　atoms　occupy　Al　sites　(2c)　,　while　V　,Cr　,Mn　,Zr　,Nb　,Mo　,Ta　and　Zn　atoms　occupy　Ti　sites　(6h).　The　site　occupation　of　elements　in　alloys　weakly　depends　on　temperature.　While　in　Ti2AlNb-based　intermetallics　,　the　predicted　results　show　that　the　site　occupying　preference　of　the　alloying　elements　V　or　Hf　is　similar　to　Ti　(8g)　,and　the　Mo　or　Ta　is　similar　to　Nb　(4c2).　The　alloys　compositions　have　no　significant　influence　on　the　site　preference　of　Al　atoms　(4c1).　The　site　occupation　of　elements　in　alloys　change　continuously　with　temperature　except　Al　,　which　means　there　is　a　second　order　character　concerning　with　the　order-disorder　transition.　Compared　with　the　study　in　literature　referring　to　special　supercell　,　the　model　employed　in　this　contribution　is　not　limited　by　the　numbers　of　component　or　the　alloy　composition.　More　additional　alloying　elements　contained　in　the　same　alloy　can　be　calculated　easily　in　a　considerable　accuracy.