This study underscores the significance of online monitoring of standard substances for bituminous coal and anthracite, two commonly used fossil fuels. Terahertz technology emerges as a powerful non-destructive detection method capable of revealing the physical and chemical properties of measured objects. In this research, terahertz time-domain spectroscopy technology was employed to investigate the spectral characteristics of four distinct types of bituminous coal and anthracite samples. The refractive index and absorption coefficient spectra of these samples were calculated across a frequency range of 0.5 THz to 2.5 THz. Furthermore, principal component analysis was conducted using all refractive index and absorption coefficient data within this frequency band. Through the analysis and comparison with known parameters of coal standard materials, it was established that carbon content primarily influences the refractive index of bituminous coal and anthracite, while ash content predominantly affects the absorption effect. These findings underscore the potential of terahertz spectroscopy in conjunction with principal component analysis to qualitatively assess the similarities and differences between coal samples, thus offering novel insights for the online monitoring of diverse coal types and qualities.