Abstract: The internal electrode materials of multilayer ceramic capacitors are gradually being replaced by base metals such as nickel, instead of precious metals. To ensure the excellent performance of the base metal internal electrode materials, the sintering process should be conducted in a reducing atmosphere. In this study, barium titanate-based ceramics samples were prepared by the solid-state method under different reducing atmospheres. The microstructure and properties of the samples were characterized using X-ray diffraction, field emission scanning electron microscope, Raman spectroscopy, and X-ray photoelectron spectroscopy. The effects of reducing atmosphere on the dielectric properties and reliability was systematically investigated. The study found that the polarization mechanism affects the dielectric properties and reliability of barium titanate-based ceramics. Specifically, With the increase of the volume fraction of H₂ in N₂ (φ(H₂)) in reducing atmosphere, the polarization mechanism transitions from short-range hopping polarization of defect charge carriers to long-range migration polarization, thus affecting the dielectric constant, dielectric loss, and insulation resistivity. The results showed that S2 exhibited a higher dielectric constant, lower dielectric loss, better insulation properties, and overall superior performance. Furthermore, barium titanate-based multilayer ceramic capacitors with thickness of 0.9 μm and the temperature coefficients of capacitance of X6S was successfully fabricated. This work provides theoretical and technical guidance for improving the dielectric properties and reliability of base metal electrode multilayer ceramic capacitors.