Based on terahertz time-domain spectroscopy, we analyze the curing properties of the adhesive layer and study the variation trend of the extinction coefficient and refractive index of the adhesive layer during the curing period. To characterize the solidification properties of multi-layer bonded structure, we employ the mean value as well as half peak half width of time-of-flight (TOF) and energy integral value of multi-layer adhesive structure after the Gaussian curve fitting. After curing for 96 h, the statistical results of the two eigenvalues gradually are stabilized. The extinction coefficient and refractive index of the adhesive layer exhibit the same trend, which proves that the curing time of the adhesive layer is approximately 96 h. We can use the two characteristic values of TOF and energy integral value adopted in this experiment as the evaluation index of the endpoint of solidification in the bonding process indirectly so as to improve the testing level of materials.