Metal-support　interactions,　which　are　related　to　electronic　metal-support　interaction　(EMSI),　particle　morphology,　interfacial　perimeter,　and　strong　metal-support　interaction　(SMSI),　have　a　strong　impact　on　the　catalytic　performance　for　ceria-supported　metal　catalysts.　High-temperature　hydrogen　reduction　can　induce　strong　metal-support　interaction　in　the　Ru/CeO2　catalyst.　However,　this　treatment　under　severe　conditions　would　lead　to　the　lowering　of　metallic　Ru　species　because　some　Ru　metal　would　be　covered　by　Ce　suboxides,　which　is　detrimental　to　the　activity　of　ammonia　synthesis　that　required　metallic　Ru　as　active　species.　Herein,　the　Ru/CeO2　catalyst　was　obtained　by　N2H4　treatment　under　mild　conditions　to　induce　a　metal-support　interaction　between　Ru　and　ceria.　The　result　shows　that　N2H4　reduction　not　only　results　in　an　enhancement　of　the　electronic　metal-support　interaction　but　also　causes　an　increase　in　the　fraction　of　metallic　Ru　and　the　amount　of　the　exposed　Ru　species.　Therefore,　a　larger　amount　as　well　as　a　lower　adsorption　strength　of　H-2　would　adsorb　on　the　Ru　catalyst.　As　a　result,　the　Ru/CeO2　catalyst　with　the　N2H4　treatment　exhibits　a　relatively　higher　ammonia　synthesis　activity.　This　discovery　offers　an　effective　way　for　the　design　of　ceria-supported　metal　catalyst　by　tuning　the　interaction　between　metal　and　ceria.　KEYWORDS:　metal-support　interaction,　ammonia　synthesis,　N2H4　treatment,　Ru/CeO2,