Abstract: The paper studied chemical structure of surface film formed under boundary lubrication condition with Scanning Auger Microprobe (SAM) ,Scanning Electron Microprobe (SEM) and X-ray Photoelectron Spectroscopy (XPS) presented a structure model of boundary lubrication film consisting of adsorpreaction film, stable reaction film and diffusion-reaction film, delt with the effect of extreme pressure additives under different conditions and gave primary analysis of formation of boundary lubrication film.