Terahertz technology has become increasingly attractive in the field of materials science due to its non-destructive and high penetration. In this study, we use terahertz time-domain spectroscopy (THz-TDS) to analyze the optical and dielectric properties of various special engineering plastics in aerospace industry. By measuring and analyzing the refractive index, absorption coefficient, and dielectric loss tangent, the results demonstrate that these special engineering plastics have unique characteristics in the terahertz frequency band. We further adopt the principal component analysis to classify different optical responses of special engineering plastics, using polyimide-imide and polysulfone as an example. This study shows that THz-TDS can be used as an effective tool to evaluate the properties and optimize the selection of special engineering plastics in aerospace industry.