Generally, the porosity of traditional Chinese medicine is measured by the destructive method of density measurement, but there is a lack of non-destructive quantification methods. As one important non-destructive method, terahertz radiation has been used to non-destructively extract the drugs' time-domain and frequency-domain optical information. For direct compression traditional Chinese medicine tablets, the effective refractive index of various tablets was obtained by different methods of terahertz time-domain signal processing and frequency-domain signal processing. It was found that the effective refractive indices with either signal processing method show a good linear relationship with the porosities of the tablets. The porosity of Puerariae Lobatae Radix tablets was extracted and modeled by linear regression based on four effective medium theory models. The porosity regression model based on the effective refractive index by time-domain signal processing shows better performance on the model interpretation and cross-validation accuracy, with the best model of the Bruggeman model (RPD=11.3325). It provides support for the process optimization of porous powder preparation of traditional Chinese medicine.