The terahertz frequency band, as an important alternative for the next generation of communication technologies, faces the challenge of rapid signal attenuation with increasing carrier frequency. Terahertz wired transmission technology is an effective means to address this issue, and precise control and optimization of material dielectric properties is the key to developing highperformance wired transmission materials in the terahertz frequency range. This paper modifies polymer materials and uses a terahertz time-domain spectroscopy system to test the dielectric properties of composite materials, studying the application of traditional dielectric constant equivalent models in the development of terahertz band materials. Based on the polarization characteristics and response mechanisms of terahertz band materials, a model and method for estimating the dielectric constant and loss tangent of composite materials in the terahertz frequency range is proposed, providing a scientific model guidance for the development of new terahertz wired transmission materials and their performance regulation.