Based on the common behavior of the Vogel-Fulcher relation followed by both dielectric dispersion of relaxor ferroelectrics in transition region and the viscosity-temperature relation for glassy liquids in supercooled state, vacancy compensation principles of donor doped barium titanate systematic ceramics are analyzed. By the introduction of the concept of configurational entropy, the temperature dependent Ti cation vacancy reaction potential is investigated, and the results show that the increase in donor content gives rise to the increase in disorder degree, the increase in Ti cation vacancy content, and the decrease in size of average polar region; on condition that configurational entropy satisfies the Vogel-Fulcher relation, Ti cation vacancy reaction regime and therefore the polar region will both increase with temperature lowing, and the variation of the regime causes dielectric dispersion of relaxor ferroelectrics. Frozen effect happens and dispersion disappears for the Ti cation vacancy reaction at a certain lower temperature.