The　first-principles　calculation　within　density-functional　theory　is　used　to　investigate　the　electronic　structures　and　magnetic　properties　in　CuHg2Ti-type　alloys　FeV2Z　(Z=Si,　Ge,　As,　Sb).　FeV2Sb　is　predicted　to　be　half-metal　and　the　energy　gap　lies　in　the　majority-spin　bands.　Though　FeV2Si,　FeV2Ge,　and　FeV2As　show　no　half-metallicity,　their　spin　polarization　of　conduction　electrons　is　around　99.7,　99.0,　and　97.8%,　respectively.　The　investigation　of　volume　distortion　shows　that　over　99%　spin-polarization　can　be　retained　in　the　range　of　5.706.05　angstrom　for　FeV2Si,　5.856.05　angstrom　for　FeV2Ge,　and　5.906.00　angstrom　for　FeV2As,　respectively.　FeV2Sb　can　keep　half-metallicity　from　6.00　to　6.15　angstrom.　We　studied　the　effects　of　defects　at　transition-metal　sites　and　Ge,　As,　and　vacancy　substitution　for　Sb　atom　on　the　electronic　structures　in　FeV2Sb,　and　the　results　indicate　that　half-metallicity　in　FeV2Sb　is　not　sensitive　to　substitutions　for　Sb　sites.　(C)　2011　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim