The effect of the induced methanation of hydrogen-treated active carbon (HTAC) support on the structural change and then catalytic activity over Ba-promoted Ru/HTAC catalysts (Ba(NO3)(2) and RnCl3 were precursors) for ammonia synthesis was investigated. It was found that a moderate degree of the methanation of HTAC support increased the catalyst surface area and pore volume significantly rather than destroyed the porous structure. But the methanation of carbon support might accelerate the growth of Ru particles, which finally led to the low activity. We suggested that both the dechlorination temperature (refer to the reductive dechlorination of RuCl3 to form Ru on HTAC) and the hydrogenolysis temperature (refer to the hydrogenolysis of Ba(NO3)(2) on Ru/HTAC) have binary effects on the catalytic activity, respectively. On the one hand, the dechlorinating effect and the hydrogenolysis effect increased with the increase of H-2 treatment temperature. On the other hand, simultaneously the methanation degree of the support increased too in above both processes. The performance of the catalyst was the combined result of the interaction of the amount of residual chlorine, Ru particle size, and the active promoter component. A respective control of the methanation degree during the catalyst preparation and activation processes was suggested to be necessary for the practical use of the promoted Ru/C catalyst.