In this study, we described a novel S-doped V2O5-WO3/TiO2 (VWTiS) catalyst that showed superior low-temperature NH3-selective catalytic reduction (SCR) activity in comparison with the VWTi catalyst. These catalysts were extensively studied by a series of characterizations and density functional theory (DFT) calculations. Results revealed that the impregnated WO3 and V2O5 species were preferentially interacting with the doped S site, which improved the electron transfer from WO3 to V2O5 and promoted the formation of reduced vanadium species. The reduced vanadium could induce large amounts of superoxide ions, which was proved as important species for NOx reduction by a benzoquinone experiment. Finally, in situ diffuse reflectance infrared Fourier transform (DRIFT) showed that S doping could promote the adsorption and activation of NH3 and NO on the VWTiS catalyst simultaneously; thus, the VWTiS catalyst exhibited superior SCR catalytic activity at low temperatures.