The　prevailing　view　of　the　deactivation　of　carbon-supported　Ru　catalyst　in　ammonia　synthesis　is　carbon　methanation,　but　those　strategies　focusing　on　inhibiting　carbon　methanation　cannot　effectively　solve　the　challenge　of　Ru/C　catalysts.　Herein　we　prepared　four　K-promoted　Ru　catalysts　with　different　Ru　loadings　and　treated　the　samples　at　450　or　500　degrees　C　under　1　MPa　during　ammonia　synthesis　reaction.　The　result　showed　that　the　presence　of　a　larger　amount　of　Ru　species　enhanced　methane　formation　at　the　reaction　temperature,　which　was　irrelevant　to　the　loss　in　activity　of　ammonia　synthesis.　On　the　contrary,　CO　formation　along　with　a　great　decline　in　catalytic　activity　can　be　observed　when　Ru　catalysts　are　heated　at　500　degrees　C.　The　characterization　results　indicated　that　the　severe　depletion　of　surface　oxygen　groups　following　the　CO-formation　pathway,　resulting　in　the　notable　decrease　in　the　amount　of　gas　adsorption,　contributed　to　the　deactivation　of　carbon-supported　Ru　catalyst.