Wolframium ions doped SrBi2Ta2O9 ceramics have been synthesized by the conventional mixed-oxide method. A sawtoothlikehysteresis loop was observed at low measuring-frequency. This phenomenon was thought to be related with the perturbationof the defect-dipole polarization under an external electrical field. A developed physical-model was derived on the basis ofsimplifying such perturbation to a simple harmonic pendulum oscillator, which combines physical considerations with thewell-known Preisach model. On the hypothesis of the simple harmonic pendulum oscillator, the included-angle between thedefect-dipole polarization and the elementary-dipole polarization can be expressed as the product of the defect-dipole relaxationvelocity and permitted relaxation time. Simulation result was excellently agreed with the observed measurement.