Considering the nucleation process was asymmetrical and not synchronous due to the effects of
defects in polycrystalline ferroelectric system, a mulriple Kolmogorov-Avrami-Ishibashi (MKAI) model was
proposed based on the classical KAI model. Moreover, the switching kinetics of Bi<sub>3.15</sub>Nd<sub>0.85</sub> Ti<sub>3</sub>O<sub>12</sub>
ferroelectric films was investigated using the MKAI model. The simulation results indicates that the MKAI
model was more consistent and exactly with experimental results.