The interactions of H2O and O2, with InP clean surface in the high vacuum chamber have been studied by means of Auger electron spectroscopy. It has been found that the water vapor plays a significant role responsible to the electron stimulated adsorption of oxygen than the pure oxygen. The In and P Auger signals change substantially during the oxygen adsorption process which is accessible as an occurence of electron stimulated oxidation (ESO). The oxygen atoms bond only with surface In atoms but not with P at the earliest stage, then they penetrate into the bulk and conbine with both In and P continually making the surface layer convert into oxide with an almost constant oxidation rate. As compared with the Auger depth profiling of InP native oxides, the similarity of the ESO and the ordinary oxidation processes is obvious. But the electron stimulated adsorpted oxygen could not fully oxidize the phosphorus in the surface layer while thermal oxidation and anodic oxidation do, the P concentration in the ESO oxide is higher than that in the thermal oxide but lower than the anodic oxide.