Terahertz time-domain spectroscopy (THz-TDS) is a spectral detection method. The information of the material is measured through the broadband terahertz pulse carrying the medium information (such as amplitude and phase). The ceramic matrix composites and silica gel materials were tested with the detection method of transmission. The optical parametric models of the material were established, and the values of the refractive index and the absorption coefficient were extracted. The curves of the refractive index and the absorption coefficient with frequency were plotted. The refractive index of the ceramic matrix composites with different density are respectively convergent to a constant of 1.11, 1.14 and 1.16, and the refractive index of silica gel with different thickness is 2.1, which is not dependent to frequency. While the frequency dependence of the absorption coefficient is evident, and the absorption of samples with different material properties is significantly different. Based on the Gaussian error theory, the errors of the optical parameters are simulated and modeled. The experimental results show that there are several error sources in the optical parameters of the ceramic matrix composites with density of 2.8 g/cm³. The standard deviation of the refractive index and the absorption coefficient are obviously related to the frequency, and the standard deviation is in the order of 0.001, which is of great significance to the precise extraction of the physical parameters such as the refractive index and the absorption coefficient.