Based on the gaussian-type distributions of bond energy and coordination number for barium titanate systematic ferroelectrics doping with a certain quantity of dopants, the bond energy and coordination number fluctuation model is used to derive the relationship between peak of dielectric constant and testing frequency. The universal Vogel-Fulcher function of the relationship is demonstrated, when the fluctuations of bond energy and coordination number approach to each other. The frozen temperature of the Vogel-Fulcher function is related only to actuation energy and relative fluctuation of bond energy. The mechanisms of dispersion due to homogenous distribution of dopants in low doping concentration and relaxor due to gaussian-type distribution of dopants over a critical concentration are investigated. It is suggested that strong inhibitory effect of substituted ions on formation and growth of ferroelectric domain is the main source of bond energy fluctuation and coordination number fluctuation.