A series of iron-samarium mixed oxide catalysts modified by zirconium, cobalt and titanium were prepared by co-precipitation method, and the effects of modified transition metal species and calcination temperature in preparation process on NH3-SCR activity were investigated. The catalysts were characterized by TG-DSC, SEM, EDS-mapping, BET, XRD, XPS, PY-IR, NH3-TPD, O-2-TPD and in situ DRIFTS. We also investigated the effects of gas hourly space velocity (GHSV), KCl, water vapor and SO2 on NH3-SCR activity over the optimal catalyst. The results indicated that the addition of transition metal could alter the activity of iron-samarium mixed oxide catalyst. In all the samples tested, titanium was illustrated to be the most suitable assistant that could increase surface acid species and acid amount, meanwhile broaden the reaction temperature window and improved the N 2 selectivity. Moreover, Ti-0.15,Sm0.075Fe0.775Ox-350 sample possessed best NO conversion rate and excellent resistance to water vapor and SO2. However, The NH3-SCR activity of K/Ti0.15Sm0.075Fe0.775Ox-350 was much lower than that of the fresh Ti0.15Sm0.075Fe0.775Ox-350. Furthermore, in situ DRIFT study verified the NH3-SCR reaction of Ti0.15Sm0.075Fe0.775Ox-350 involved both E--R mechanism and L-H mechanism.