Nano-ZnO samples with different sizes were synthesized in the amorphous SiO2 network by hydrolysis of tetraethyl orthosilicate(TEOS).X-ray diffraction(XRD) patterns reveal that the average size of nano-ZnO decreases from ～14.6 nm to 1.9 nm with the increase of TEOS amount.Photoluminescence(PL) spectra in the visible region show that the peak position presents blue-shift from ～560 nm to 510 nm and the emission intensity is significantly enhanced.From analysis of ultraviolet-visible(UV-VIS) absorption spectra,PL spectra and energy-level structure of nano-ZnO and amorphous SiO2,we find that the luminescence enhancement is due to association with the surface bonding on ZnO,which inhibits non-radiative transition process and the reabsorbed process between nano-ZnO and amorphous SiO2.In addition,the reduced distance between photo-induced electrons at nano-ZnO surface and internal oxygen vacancies enhances the radiative transition probability and then the luminescent intensity when the average particle size decreases.