The effects of temperature and time of reductive dechlorination of RuCl3 to remove negative-effected chlorine and then form metallic Ru on hydrogen-treated active carbon (HTAC) support on catalytic activity for ammonia synthesis were investigated in detail. The purpose was to try to prepare Ru catalyst by using the low-cost RuCl3 as a precursor to replace other high-priced chlorine-free Ru compounds that have commonly been used as precursors. TG-MS spectra indicated that the reductive dechlorination of RuCl3/HTAC to form Ru/HTAC under H-2 started at 220 degreesC and seemed to finish around 350 degreesC. But elemental analysis disclosed that there were still 0.08 and 0.05 wt.% of chlorine left on 5 wt.% Ru/HTAC even after the reductive dechlorination at 450 and 600 degreesC for 24 h, respectively. However, the methanation of carbon support was induced when the dechlorination temperature was higher than 475 degreesC. Activity results showed that a moderate dechlorination condition of 450 degreesC for 24 h led to the highest activity for the obtained Ru/HTAC catalyst promoted by Ba(NO3)(2). Therefore, we proposed that to control the induced methanation to avoid the destruction of catalyst was more important than to diminish the small amount of chlorine remaining on Ru/HTAC that required a higher temperature than 475 degreesC. This activity was almost the same as that of the catalyst prepared from the chlorine-free Ru(acac)(3). Therefore, this new preparation method was proved to be empirically practicable and theoretically reasonable.