As the internal electrode materials in multilayer ceramic capacitors (MLCCs) are increasingly being replaced by base metals such as nickel instead of precious metals, the sintering process must be conducted in a reducing atmosphere. This work investigates the properties of Mn-doped BaTiO3-based ceramics sintered under different reducing atmospheres, exploring the effect of varying H?/N? ratios on dielectric performance and reliability. BaTiO3-based ceramics were prepared using the solid-phase method under different reducing atmospheres. X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the microstructure and properties of the samples. The study found that the polarization mechanism significantly affects the dielectric performance and reliability of BaTiO3-based ceramics. Specifically, as the reducing atmosphere intensifies, the polarization mechanism transitions from short-range defect dipole polarization to long-range defect carrier polarization, impacting the dielectric constant, dielectric loss, and insulation resistance. The sample sintered under 1.5% H?/98.5% N? (S2) exhibited the highest dielectric constant, lowest dielectric loss, and best insulation resistance, demonstrating excellent overall performance. Additionally, BaTiO3-based MLCCs with thickness of 0.9 μm and the TCC of X7R were successfully fabricated. This work provides theoretical and technical guidance for improving the dielectric performance and reliability of BME-MLCCs.