To resolve the problem of phase separation in PMMA/SiO2 hybrids system, different polymethyl methacrylate(PMMA)/SiO2 hybrids were prepared by synchronous sol-gel process. There is a covalent bond between PMMA and SiO2. The samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD ), Fourier transformed infrared spectrum (FTIR) and thermal gravity(TG). The results show that when the silica content is between 20%~60%, there is no phase separation in the PMMA/SiO2 hybrid system.and the transparency of PMMA/SiO2 hybrid material is good when the silica content is between 20%~40%.