The chemical state variation of Cu element and its influencing factors on Cu modified vanadium-based de-NOx catalyst were investigated by X-ray photoelectron spectrometry(XPS).The results showed that Cu element in catalyst existed in the forms of CuO and Cu2O,and CuO could be reduced under X-ray irradiation.However,the initially observed Cu2O was mainly derived from the prepared samples other than generated by X-ray.The influencing factors for the reduction from CuO to Cu2O included the irradiation time and power of X-ray,copper load and sample preparation methods,etc.The results indicated that the reduction percentage for CuO increased gradually with the increase of irradiation time or power of X-ray.In general,the reduction percentage for CuO decreased with the increase of Cu load.The reduction percentage for CuO keeped at the level about 1.2%when the Cu load reached to 3%.The existence of the active component vanadium increased the reduction activity of CuO,while the addition of oxalic acid reduced the reduction activity.This study provided an important reference for the characterization and analysis of Cu modified vanadium denitrification catalyst,and also gave some suggestions for parameter settings and analysis method for other similar X-ray sensitive samples.