Minimizing　the　dosage　of　toxic　SeO2　additive　in　electrolyte　for　electrochemical　deposition　of　metal　manganese　without　compromising　the　current　efficiency　has　long　been　the　desire　for　electrolytic　manganese　industry.　Herein,　by　combinative　usage　of　SeO2　and　gluconic　acid　(GlcA)　as　the　composite　additives,　50　%　of　SeO2　dosage　can　be　cut　down　while　the　current　efficiency　can　be　increased　from　67　%　to　90　%　at　the　same　time,　realizing　the　energy　consumption　being　reduced　by　23　%　at　the　optimized　concentration　of　1.84　g/L　GlcA.　The　electrochemical　tests　and　electrode　surface　characterizations　as　well　as　density　functional　theory　calculations　jointly　imply　that　the　addition　of　GlcA　can　greatly　increase　the　diffusion　coefficient　of　Mn2+　from　1.5　x　10-6　cm2/s　to　5.6　x　10-　5　cm2/s,　accelerating　the　approaching　of　Mn2+　towards　the　electrode　surface　by　decreasing　the　diffusion　barrier　energy　from　17.93　kJ/mol　to　11.51　kJ/mol.　On　the　electrode　surface,　the　SeO32-　is　responsible　for　facilitating　the　electrochemical　deposition　of　metal　Mn　by　forming　the　MnSe　intermediate　while　GlcA　is　in　charge　of　restraining　the　activation　of　H2O　molecule　for　inhibiting　H2　generation,　synergistically　contributing　to　the　efficient　production　of　electrolytic　metal　manganese.　The　results　can　provide　new　insights　for　the　environmentally　friendly　and　high-efficiency　upgrading　of　manganese　industry.