Fine-grained BaTiO3-based ceramics with core-shell structures were prepared using the chemical coating method and the solid-state method. The sintering behavior and microstructure evolution were investigated for the samples prepared using different methods. The dielectric properties of modified BaTiO3 ceramics were also investigated, and the TEM-EDS results provided a detailed explanation for the different temperature coefficient of capacitance behaviors. In addition, the insulation resistivity for the ceramic samples under elevated temperature and high voltages was observed. The highly accelerated lifetime test results indicate that the samples prepared by the chemical coating method exhibited higher insulation resistance and a smaller degradation rate. Impedance analysis demonstrated that the grain boundary activation energy was much higher for the samples prepared by the chemical coating method.