This　paper　investigated　Mg2+　enhancement　of　biomass　production　through　regulating　the　generation　and　use　of　energy　in　Rubrivivax　gelatinosus　wastewater　treatment.　Results　showed　that　proper　Mg2+　dosage　range　was　1.5-15mg/L.　With　optimal　Mg2+　dosage　(10mg/L),　biomass　production　(5010mg/L)　was　improved　by　60%.　Both　protein　and　chemical　oxygen　demand　(COD)　removals　reached　above　90%.　Biomass　yield　improved　by　38%.　Hydraulic　retention　time　was　shortened　by　25%.　Mechanism　analysis　indicated　that　as　activator,　Mg2+　promoted　specifically　isocitrate　dehydrogenase　(IDH)　and　Ca2+/Mg2+-ATPase　activities　in　energy　metabolism,　and　then　improved　the　generation　of　adenosine　triphosphate　(ATP)　and　the　use　of　ATP.　This　enhanced　the　secretion　and　activity　of　protease,　protein　and　COD　removals,　and　then　led　to　more　biomass　production.　With　10mg/L　Mg2+,　IDH　and　Ca2+/Mg2+-ATPase　activities,　ATP　production,　protease　activity　were　improved　by　43.8%,　40.6%,　39.4%　and　46.5%,　respectively.