We investigate the oxidation behavior of Si1-xGex alloys ( x=0005，002，005，015 and 025). A new ellipsometric method is used f or the generating and measuring Ge nanostructures in oxidation of SiGe alloys. The fundamental optical constants of Ge nanolayers in the sample were determined by ellipsometry. The thickness and origin of the Ge bi_nanolayer were found. A new peak in photoluminescence PL spectra was discovered, which is related to the Ge bi_nanolayer (thickness: 08—14nm). Some suitable model and calculating formula can be provided with the UHFR method and quantum confinement analysis to interprete the PL spectrum and the nanostructure mechanism in the oxide.