Site　preference,　tetragonal　distortion　and　phase　stability　of　all　d-metal　Heusler　alloys　Mn2-xNi1.5+xV0.5　(x　=　0,　0.5,　1),　Mn2-xNi1+xV　(x　=　0,　0.25,　0.5,　0.75,　1)　and　Mn2-xNi0.5+xV1.5　(x　=　0,　0.5,　1,　1.5)　are　investigated.　It　has　been　found　that　Ni2MnV　is　stable　in　Hg2CuTi-type　Heusler　structure,　while　Mn2NiV　tends　to　crystallize　into　Cu2MnAl-type　Heusler　structure.　Mn　atoms　in　both　Ni-rich　and　Mn-rich　Mn-Ni-V　alloys　preferentially　occupy　A,　C　sites,　suggesting　that　the　site　occupation　in　Mn-Ni-V　ternary　alloy　is　not　following　the　conventional　site　preference　rule.　A　potential　tetragonal　distortion　is　expected　in　cubic　structure　of　Ni-rich　alloys　MnNi2V,　Mn1.25Ni1.75V,　MnNi2.5V0.5　and　Mn0.5Ni2V1.5.　It　is　found　that　the　tetragonal　distortion　is　mainly　attributed　to　the　decrease　of　intensity　for　DOS　at　the　Fermi　level　in　the　minority　spin　direction　which　is　caused　by　the　splitting　of　peaks.　This　study　will　guide　us　to　design　new　tetragonal　Heusler　materials　for　spintronic　devices.