Interface evolution of nanometer scale Au-Ag bimetal film on SiO2 substrate surface during electromigration was investigated by angle resolved X-ray photoelectron spectroscopy (ARXPS). ARXPS spectra showed that a chemical reaction between Au-Ag film and SiO2 layer occurred at interface, which caused Au, Ag and Si having different distribution and chemical states across the film. This result as well as previous observation by atomic force microscopy (AFM) demonstrate that electromigration of Au-Ag bimetal film on SiO2 surface is accompanied with strong interfacial chemical reaction rather than a simple lateral physical diffusion process.