In this paper, superfine SiO₂ nanoparticles are utilized as composite abrasive additive to improve the polishing property of CeO_2, which is prepared through chemical precipitation method by rare-earth chloride as raw materials, silicofluoric acid as fluoride, Na₂CO₃ as modifier, and NH₄HCO₃ as precipitator. XRD, SEM, particle size analyzer, and atomic force microscopy are applied to characterize the physical structure, morphology, and size distribution. Furthermore, the as-prepared composite abrasive is used to perform chemical mechanical polishing (CMP) experiment on K9 glass to identify the impact of different mass fraction of SiO₂ on the CMP property of work materials. The results show that the composite abrasive contained 0.5% SiO₂ has the best polishing property, the surface roughness, and material removal rate of glass after polishing can reach at 1.3157 nm and 22.6 nm/min, respectively.