Arsenic (As) is found to be poisonous to the commercial V2O5-WO3/TiO2 catalysts for selective catalytic reduction of NOx with NH3. The NOx conversion of catalysts declines and N2O formation dominates at high temperature (above 300 degrees C) after As poisoning. A series of activity and characterization experiments are applied to reveal the deactivation mechanism caused by As. Results indicate that doping of As on the catalysts, which exists as H2AsO4- and HAsO42-, doesn't seriously change surface area of catalysts or TiO2 phase, but greatly decreases both the Lewis and Bronsted acid sites. It is found that V-OH is destroyed and less reactive As-OH is newly formed. V-OH site is crucial to the NH3 adsorption and its destruction by As contributes to catalyst deactivation. Besides, stronger oxidizability of catalysts that resulted from more surface-active oxygen aroused by As leads to substantial non-selective catalytic reduction reaction and NH3 oxidation at high temperature. Both of these two aspects result in lower NOx conversion and higher N2O formation. However, SO42- can provide remarkable surface acidities and the sites that destroyed by As can thus be supplied. Benefited from these new reactive acid sites, catalysts with prominent SO42- loading show superior arsenic resistance even with a high As content, which indicate to be a promising anti-poisoning formula. Finally, mechanism of arsenic poisoning and resistance effect of SO is proposed based on the above analysis. (C) 2016 Published by Elsevier B.V.