La-Ba-K-Ru/AC　catalysts　for　ammonia　synthesis　were　prepared　by　co-impregnation　method　using　graphited　active-carbon　as　the　support　and　water-soluble　chloride-free　Ru　complex　as　the　precursor.　The　results　demonstrate　that　the　La　promoted　Ba-K-Ru/AC　catalysts　exhibit　good　catalytic　activity,　high　thermal　stability　and　strong　resistance　against　methanation.　TEM　(Transmission　Electron　Microscope)　and　CO　(carbon　monoxide)　chemisorption　analysis　indicate　that　the　Ru　particles　had　a　relatively　uniform　size　of　3　similar　to　5　nm　and　the　particle　surface　might　be　partially　covered　by　LaOx　and　BaOx.　H2-TPR　(Temperature　Programmed　Reduction)　results　suggest　that　strong　interactions　might　exist　between　the　Ru　particles　and　the　promoters　(La　and　Ba).　The　N-2-TPD　(Temperature　Programmed　Desorption)　and　H-2-TPD　measurements　show　that　the　presence　of　small　amount　of　La　enhances　the　adsorption　of　N-2　and　inhibits　the　adsorption　of　H-2,　resulting　in　higher　TOF　values　and　better　catalytic　performances.　Moreover,　no　obvious　agglomeration　of　Ru　particles　was　observed　on　the　catalysts　after　heat　resistance.　The　superior　catalytic　stability　of　La-Ba-K-Ru/AC　is　associated　with　its　strong　resistance　against　methanation　of　active-carbon　due　to　highly　coverage　of　ruthenium　surface　and　strong　inhibition　of　hydrogen　by　promoters.