As electronic devices continue to miniaturize, improving the dielectric performance and reliability of Multilayer Ceramic Capacitors (MLCC) during ultra-thin layer development has become a critical challenge. This study achieved significant optimization of BaTiO₃-based ceramic dielectric layers in ultra-thin MLCCs through precise control of the "core-shell" structure. Research shows that adjusting Ho doping concentration can effectively regulate the characteristics of the "core-shell" structure, thereby optimizing the dielectric performance and reliability indicators of MLCCs. When the Ho doping concentration reaches 1.5 mol%, the shell concentration increases significantly, and the material exhibits excellent dielectric properties: room temperature dielectric constant reaches 3820, dielectric loss remains below 2.0%, and demonstrates outstanding temperature stability with a temperature coefficient of capacitance not exceeding 15% within the -55 ℃ to 100 ℃ range. Notably, when Ho doping increases to 2 mol%, although the increased shell thickness leads to changes in the core-shell ratio resulting in slightly decreased dielectric performance, the material's insulation resistance improves significantly, enhancing overall reliability. This study systematically elucidates the structure-property relationships among Ho doping concentration, "core-shell" structural characteristics, and material performance, providing important theoretical guidance and experimental foundation for the structural design and performance optimization of ultra-thin MLCC dielectric materials. These findings hold significant scientific and practical value for advancing the development of next-generation high-performance MLCCs.