Abstract: Nano-sized SiO₂ was surface modified with silane coupling agent KH-570. The modified nano SiO₂ was studied by means of infrared spectrometer (IR), thermogravimetric (TA), Zeta potential, SEM. The results showed that coupling agent KH-570 and SiO₂ form a Si-O-Si bond with 5. 8% attached amount and 10. 35% of the solvent water; Zeta potential of modified nano SiO₂ in ethanol medium reduced from -14. 9 mV to -41. 1 mV, the system stability can reach more than 60 h. Used as photocureable dental composite resin filler, the dispersion is remarkably improved, the vickers hardness, compression strength, elastic physical properties such as flexural strength increased more than 10%.