The promotional effect of Co on Cr-Ce catalyst for the selective catalytic reduction of NH3 to N2 was investigated. The catalytic activity and SO2 tolerance of Cr-Ce catalyst were greatly enhanced by the addition of 5wt% Co, in the temperature range of 250oC-350oC. And the N2 selective of Cr-Ce had been highly enhanced from 40 to 98% at 240oC. With addition of Co, Ce4+ species on surface was led to a better dispersion, as a result the redox properties of the catalysis was enhanced. Moreover, Co carried out the reaction towards the conversion of N2, the 5wt% Co/Ce-Cr catalyst reduced the formation of NH4NO2, and the SCR reaction over Co/Cr-Ce followed the Eley-Rideal mechanism.