Ti2AlNb-based　alloy　with　a　dominated　orthorhombic　phase　is　one　of　the　most　promising　high-temperature　structural　materials.　In　this　work,　the　equilibrium　volume,　elastic,　and　thermodynamic　properties　of　the　ordered　O　phase　with　stoichiometric　Ti2AlNb　were　predicted　under　different　temperatures　using　first-principles　calculations　based　on　density　functional　theory　combined　with　quasi-harmonic　approximation　(QHA).　With　the　increase　of　temperature　from　0　to　1300　K,　the　elastic　properties　decrease　moderately　and　the　bonding　strength　weakens　slightly.　The　intrinsic　properties　of　the　Ti2AlNb　O　phase　are　ductile　at　all　temperature　considered.　In　order　to　explore　the　evolution　mechanism　of　the　temperature-dependent　elastic　properties　further,　the　density　of　state　(DOS)　has　been　analyzed.　The　stoichiometric　Ti2AlNb　O　phase　shows　good　high-temperature　mechanical　and　thermal　stability,　which　is　a　kind　of　potential　high-temperature　alloy　applied　in　aeronautics　industries.　(C)　2017　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim