Using high temperature scanning tunneling microscopy (STM) and XPS, we investigated the dynamic process of SrO/Si(100) changing to Sr/Si(100) reconstructed surface, which plays a critical role in the growth of crystalline oxide on silicon substrate. During this process we find some interesting phenomenan: there appears crystalline SrO on Si(100) substrate at low annealing temperature of 500 ℃; at higher annealing temperature of 550—590 ℃, the oxygen in the SrO/Si(100) interface will react with silicon and form volatile SiO, leading the surface with a large quantity of line vacancies. In the later case, there appears abnormal metallic property of this surface, which results from dangling bonds of silicon atoms in the surface.