In this work, the pulse type therahertz time domain spectroscopy (THz–TDS) system was used for measuring the refractive index and thickness of EMC mold non-desructively. Based on terahertz time domain signals of transmission and normal mode, a theoretical model was developed to measure the refractive index of EMC Mold without measuring the thickness of EMC mold. In order to reduce the error that may occur when measuring therahertz signal, interpolation was applied to calculate the time delay. The refractive index of EMC Mold was measured using THZ-TDS system. At the same time, the thickenss of EMC Mold was calculated and compared to actual thickness which was measured through SEM.