Using　the　ab　initio　method　and　natural　bond　analysis,　the　reactivity　and　chemical　bond　of　dinuclear　molybdenum　sulfur　clusters　with　Mo(2)OnS(4-n)　(n　=　1-3)　core　were　studied.　The　results　show　that　the　Mo-Mo　bonds　in　these　clusters　are　significantly　affected　by　the　delocalization　effects　of　the　multicenter　d-p　pi　and　pi(Mo　-　X-t)　bonds,　besides　the　direct　interactions　between　Mo　atoms.　The　substitution　reactions　of　the　cluster　core　are　also　discussed,　and　it　is　indicated　thar　sulfur　atoms　have　a　preference　for　the　bridging　sites　and　the　oxygen　atoms　tend　to　attach　to　the　terminal　sites.