Lightweight　high-entropy　alloys　(LHEAs)　with　low　density　and　high　strength　are　considered　to　be　the　next　generation　of　lightweight　materials.　Al-Cr-Mo-Ti-based　LHEAs,　in　particular,　have　gained　intensive　attention　due　to　their　excellent　mechanical　properties　and　high-temperature　oxidation　resistance.　This　study　investigates　the　lattice　distortion,　mechanical　properties,　and　surface　oxidation　mechanism　of　BCC_AlCrMoTi　and　AlCrMoTiV　LHEAs　based　on　site　preference.　The　relative　lattice　distortions　of　BCC_AlCrMoTi　and　AlCrMoTiV　LHEAs　were　calculated　to　be　4.78%　and　6.12%,　respectively,　with　corresponding　hardness　values　of　628.50　HV　and　553.20　HV.　The　results　indicate　that　the　addition　of　V　exacerbates　lattice　distortion,　thereby　inducing　the　alloy　softening.　Surface　oxygen　adsorption　energy　calculations　demonstrate　significant　variations　at　hollow　sites,　with　Ti　and　V　atoms　exhibiting　stronger　adsorption.　As　surface　oxygen　coverage　increases,　the　work　function　of　both　alloys　increases　gradually.　Notably,　the　BCC_AlCrMoTiV　LHEA　consistently　exhibits　higher　surface　work　function　and　average　adsorption　energy,　suggesting　that　the　addition　of　V　reduces　the　surface　oxidation　activity.　Analysis　of　the　electronic　structure　reveals　the　shift　in　adsorption　sites　of　O　atoms　and　the　reduced　capacity　for　successive　O　atom　adsorption.　This　study　provides　valuable　insights　for　the　mechanical　properties　and　oxidation　behaviors　of　Al-Cr-Mo-Ti-based　LHEAs.　©　2025　Elsevier　B.V.