We investgated the oxidation behaviors of Si1-xGex alloys with 0.5%, 2%, 5%, 15% and 25%) Ge content. The oxidation of SiGc films with different compositions was carried out in dry oxygen gas at 800℃, 900℃ and 1000℃ for various length of time. Thickness and property of nanoparticle and nanolayer in oxide films and germanium segregation in oxidation of SiGe alloys obtained using high precision ellipsometer (HPE) showed good agreement with Rutherford backscattering spectrometry (RBS), profile dektak instrument (PDI) and high-resolution scanning transmission electron microscopy (HR-STEM) observation. We observed that the Ge content in the oxide layer increased with the Ge content in SiGe layers, Ge content in the oxide film decreased with the increase of oxidation temperature and with the increase of time length. Rejection of Ge resulted in piling up of Ge at the interface between the growing SiO2 and the remaining SiGe which formed nanometer Ge-rich layer. And substantial interdiffusion of Si and Ge took place in the remaining SiGe which led to the complicated distribution of Ge segregation.Several new phenomena were discovered,and the experimental results were dicussed and simulated.The oxidation optimum of SiGe has been obtained.