The influence of thermal aging on catalytic activity, weight loss, phase structure, surface area and pore characteristic of commercial V2O5-WO3-TiO2 selective catalytic reduction (SCR) catalyst were investigated using a fixed bed reactor, TG-DTA, XRD and nitrogen adsorption. The catalyst showed good catalytic activity and thermal stability in fresh state or aging for 50 h at 550 °C and 650 °C in air. The catalyst drastically deactivation after calcination for 50 h at 650 °C in air, the maximum conversion of NO dramatically decreased from 100 to 60 %, the light off temperature increased from 187 to 360 °C. The analysis revealed that the deactivation of catalyst was caused by three factors. Firstly, the reduction of vanadia loading was caused by the vocalization; secondly, the reduction of the active site was resulted from the interaction V2O5 with TiO2 and lastly, the changes of reaction area and pore structure were due to the phase transformation of TiO2 from anatase to rutile.