Abstract: In order to interpret the chemical state of elements on impregnated barium tungsten cathodes, synchrotron radiation photoelectron spectroscopy (SRPES) are used to investigate the surface of an impregnated barium tungsten cathode. The result indicates, compared with the situation before activation, after 1150℃× 90min high temperature activation, the thickness of absorbed layer of cathode surface reduces remarkably, absorbed C disappears totally, O content rises obviously, W content increases at double,Ba content increases by 2 times on the barium tungsten cathode surface; In addition, the remarkable chemical shifts of spectrum peaks of elements such as O1s, W4f and Ba3d occur toward larger binding energy on the cathode surface. With further analysis, after activation, W surface and Ba atoms are absorbed and oxidized by absorbed oxygen distributing on the cathode surface, Ba exists in the form of absorbed chemical compound Ba_m?O_n (m≤n)