In coal-fired power plants, selective catalytic de-NO_x systems are widely used and offer a very efficient method to reduce NO_x emissions from such plants. However, de-NO_x catalyst degrades in long-term operation and catalysts must be periodically exchanged. Exchange of catalysts costs a great deal, hence there is a strong economic incentive to elucidate the degradation mechanism of catalysts and optimize the operation conditions of de-NO_x equipment. In this study, fluorescent X-ray analysis is performed to investigate the elemental distribution on the catalyst surface. Also, X-ray absorption fine structure (XAFS) analysis is applied to determine the chemical form of Vanadium in the catalyst. The results show that elements found in fly ash are detectable in the upstream region near the inlet, whereas such elements are not detected in the downstream region near the outlet. This tendency is in good qualitative agreement with the author's previous numerical result. Vanadium in the fresh catalyst is mainly in its 3+ valence state, whereas that in used catalyst is mainly in the 4+ or 5+ valence states. The ratio of vanadium in 5+ valence state is larger in the inlet region than in the downstream region. This is due to turbulent eddy mixing which promotes vanadium oxidation in the inlet region.