In recent years, Ultra-Thin Glass (UTG) has attracted substantial market attention due to its multi-scenario applications. One of the technical cores in UTG manufacturing is the abrasive design of the chemical mechanical polishing (CMP) process. The present work proposed rare-earth-doped core–shell structured PS@CeO₂, PS@CeO₂:La, and PS@CeO₂:Yb abrasives synthesized by a low-temperature two-step method. The core–shell abrasives are large uniform nanospheres with a size of about 375 nm ∼ 450 nm. According to the matching effect of RE³⁺ radii and defect sizes, La³⁺ with larger radii exhibits a more substantial modulation effect than Yb³⁺ upon the lattice distortion and Ce³⁺/Ce⁴⁺ chemical shift. The CMP results revealed the superior polishing efficiency and better flattening ability of core–shell abrasives. The optimized PS@CeO₂:La shows the best glass polishing ability (MRR = 480.22 nm/min, Ra = 0.32 nm), which is attributed to the increased Ce³⁺ composition from 9.79% to 28.14% (compared with the pristine PS@CeO₂) and large particle size, indicative of potential applications of novel abrasive systems in the field of glass polishing.