The core-shell structure formed by coating can enhance the uniformity of particles within ZnO varistors, which is conducive to the improvement of their microstructure and comprehensive performance. In this study, the ZnO@Bi2O3 core-shell structure powder was prepared by chemical precipitation and calcination purification, and doped with Sb2O3 to form the ZnO@Bi2O3-Sb2O3 (ZBS) system powder, which was then compared with the doped sample. The alloying method was combined with high-temperature X-ray diffraction (HT-XRD) to investigate the phase evolution and its pattern, while scanning electron microscopy (SEM) and X-ray fluorescence (XRF) were employed to characterise the microstructure and elemental distribution. It was observed that the phase evolution of the ZBS system can be divided into two main stages: the generation of pyrochlore and its subsequent transformation to spinel. It is observed that Bi₂O₃ in the core-shell structure samples exhibits a certain selectivity for the reaction that generates the pyrochlore phase. Furthermore, the onset temperature of pyrochlore-to-spinel transformation is lower than that of the doped samples by 80–100 °C, and the reaction rate is faster. Base on the microstructural results, it was found that the core-shell structure powder spinel was more uniformly distributed with a smaller average grain size up to 5.074 μm and a more well-distributed particle size. The influence of the core-shell structure on the high-temperature sintering of ZnO varistor ceramics was discussed in terms of phase situation and microstructure.