The　effect　of　alkaline-earth　oxides　as　promoters　on　Ru/AC　(AC　=　activated　carbon)　catalysts　was　explored.　Alkaline-earth　metal　oxides　can　reduce　the　agglomeration　of　ruthenium　particles　at　high　temperatures,　which　increases　the　amount　of　available　ruthenium.　The　influence　of　the　Mg　promoter　on　the　distribution　and　activity　of　the　Ru/AC　catalyst　were　investigated　by　CO　chemisorption,　X-ray　diffraction,　and　energy　dispersive　spectrometry　and　by　an　activity　test　for　ammonia　synthesis.　The　results　show　that　a　specific　quantity　of　magnesium　significantly　promotes　the　uniform　distribution　of　Ba　and　Ru　on　the　surface　of　AC,　which　enhances　catalytic　activity.　The　introduction　of　Mg　significantly　improved　the　size　of　the　Ru　particles　and　increased　the　Ru　surface　area.　The　distribution　and　interaction　were　improved　greatly　for　the　Ba　promoter　and　the　Ru　precursor　on　the　surface　of　the　AC　because　of　the　addition　of　the　Mg　promoter.　The　introduction　of　magnesium　to　Ru-Ba-K/AC　significantly　improved　the　utilization　ratio　of　the　noble　metals　and　the　performance-price　ratio.