Abstract: In order to investigate the diffusion and transition mechanism for Ag in Ag-Al supersaturated solid under oxygen atmosphere, the diffusion rate, temperature and process for Ag-Al-O phase transition were calculated by the molecular dynamics simulation. The calculated results show that there are conflict between precipitation of Ag and formation of compact alumina film during oxidation process, Ag precipitates quickly at 600 K in oxygen atmosphere, associated with the formation of the Ag₂Al phase in Al-Ag solution. The model and calculation result were proved to be reasonable through experiment, Ag in nano scale could be controlled through the short path diffusion of Ag and formation of compact alumina film under reaction temperature。