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In this study, barium calcium zirconate titanate nanoparticles and nanofibers (denoted as BZT-BCT NPs and BZT-BCT NFs, respectively) were prepared by the sol–gel method and electrospinning, respectively. Under different temperatures and frequencies, the dielectric spectra of polyvinylidene fluoride (PVDF), BZT-BCT NPs, and BZT-BCT NFs composites were measured. On the basis of the experimental data, the polarisation activation energies of the polymer matrix interfacial polarisation and the dipole turn polarisation were calculated, and the basic polarisation characteristic parameters of the polymer matrix materials and fillers were obtained. Moreover, the effects of the filling phase and filling ratio on the dielectric properties of the composites were studied through applying BZT-BCT NPs and BZT-BCT NFs as the filling phases of the PVDF matrix and PVDF matrix composites. Furthermore, the double-layer low-density polyethylene (LDPE)/PVDF composites as well as the LDPE/PVDF composites uniformly mixed at a volume fraction of 1:1 were prepared, and the interfacial polarisation behaviours of the two materials were studied by dielectric spectroscopy to establish an effective analytical method so as to characterize interfacial polarisation established. The experimental results revealed as follows: interfacial polarisation was a significant mechanism of the polarisation behaviour of the composite materials; the fillers with different shape factors had varying effects on the dielectric constant of composites; meanwhile, the dielectric constant of the composite conformed to the predictions of the effective medium theory model.