Abstract: Why a layer of Os film with high work function can increase the emission ability of impregnated cathode notably? This is an undecided important problem for a long time. In this article, based on the emission test and scanning electron microscope analyzing, the Synchronous Radiation PhotoelEctron Spectrum (SRPES) technology is used to measure element composition and chemical states on W-film cathodes and Os-film cathodes. The results indicate, the emission ability of the cathode coated with Os-film is higher than that coated with W-film by 1.65 times, and Os-film can increase the number of barium atom and low binding energy oxygen atom on the surface of cathodes by 40% and 56% comparing to W-film. With further analysis, the low melting point and characteristics apt to resolve for the oxides of Os film, accelerate the transformation of oxygen on cathode surface during activation, thus cause the Os-film cathode surface to get more surplus barium Ba+(a) and to get higher emission ability.