A sequence of Cr-modified CeZr2Ox catalysts were synthesized through the co-precipitation way and applied in selective catalytic reduction (SCR) of NOx with ammonia. The optimal catalyst (Cr1CeZr2Ox) exhibited the excellent NH3-SCR activity and high SO2 resistance. From the characterization results, Cr species in Cr1CeZr2Ox could suppress the formation of ZrO2 crystals, which could also contribute to stronger surface acidity and reducibility. Besides, more Ce3+ and surface adsorbed oxygen species were observed on Cr1CeZr2Ox catalyst. On the basis of in situ DRIFT experiments, it could be confirmed that the NH3-SCR process on Cr1CeZr2Ox was promoted through Langmuir-Hinshelwood (L-H) mechanism. Besides, the improved NO oxidation and more ad-NOx and ad-NH3 also played a vital role for the superior low-temperature SCR activity of Cr1CeZr2Ox.