[en] Highlights: • Colossal permittivity (66886) is achieved in this system by doping Nb₂O₅ and sintering in reducing atmosphere synchronously. • The self-compensation mechanism is revealed in BaTiO₃ ceramics according to different content of Nb₂O₅. • The internal polarization mode is adjusted, and the mechanism of different polarization is revealed. -- Abstract: Based on adjusting the relationship between polarization and charge carriers, barium titanate (BaTiO₃) ceramics with colossal permittivity and high insulation resistivity are prepared by solid-state reaction approach. Modified by reducing atmosphere (0.1%H₂/N₂) and donor-ions doping, different polarization modes are discussed via treatment with impedance analysis and dielectric data, then the relationship between dielectric properties and charge carriers is established. It is illustrated that the interfacial polarization and hopping polarization can be adjusted along with different charge compensation modes by changing Nb⁵⁺ content from 0.5 mol% to 3 mol%, corresponding to colossal permittivity and insulation resistivity, respectively. Thus, the approach provides an adjustable mechanism for balancing the colossal permittivity and insulation resistivity in BaTiO₃ ceramics. The colossal permittivity can be achieved by controlling oxygen vacancies, and the distribution of oxygen vacancies is further adjusted by the donor-ions. Meanwhile, the self-compensation is found in the grains to improve the grain resistance. On this basis, single-layer microchip capacitors of BaTiO₃-based ceramics are available in the future.