The optical response characteristics of poly (vinylidene fluoride) (PVDF) are important for its wide applications in sensing and energy harvesting. A Terahertz Time-Domain Spectroscopy (THz-TDS) system was utilized to measure the optical constants of two types of PVDF piezoelectric materials in the terahertz frequency range. The optical characteristics of PVDF were determined under the experimental conditions of weak and strong terahertz field. The optical response characteristics of samples fabricated through the hot-pressing and melt-extrusion methods were analyzed. The results indicate that samples produced by the hot-pressing method exhibits stronger optical response signals, while those fabricated by the method of melt-extrusion displays weaker ones, which can be attributed to the thicker domain walls. To elucidate the underlying physical mechanisms responsible for these observed differences in optical response characteristics, the samples were measured by X-ray diffraction (XRD) technique. This analysis reveals that the variations in crystal structures among the samples lead to differences in polarity. These structural differences significantly impact the optical properties under strong terahertz fields. The findings provide valuable theoretical and experimental insights for the practical application of PVDF-based materials.