Based on reversion motion of dipoles in ferroelectrics under the electric field in the random field Ising model, the relationship between electric field and polarization in order-disorder transition is investigated, and the function tanh(x) for the electric field in order-disorder transition is coincident with the experimental relationship between electric field and polarization in the second order ferroelectric transition. Therefore, increases in polarization and internal poling field are due to the collective motion of dipoles, where electric field and temperature are critical in the polarization and Gibbs free energy. By distinguishing the contributions between optic mode and polarization portion with a gaussian-type distribution of Curie-temperature, and considering a complex dispersion form of dielectric permittivity contributed by dipoles, the relationships between dielectric permittivity and temperature, as well as frequency, are derived.