In this study, the undamaged and damaged areas in fused silica induced by laser with different energies were tested with the transmission terahertz time-domain spectral system. The time domain signal and frequency spectra of 0.8-1.25 THz are obtained. The peak-to-peak value, amplitude, transmission spectrum, refractive index, and absorbance are analyzed. The results show that the peak-to-peak value, amplitude, transmission spectrum, and refractive index of the damaged area are obviously reduced compared with those of the undamaged area, and with the increase of laser energy and the enlargement of damaged area, these parameters gradually decrease. In contrast, the absorbance exhibits an opposite change. Therefore, the variation in the optical properties of fused silica in the terahertz wave band could be applied to distinguish the damages and analyze the degree of damage, which provides a good basis for applying the terahertz time domain spectral technique to the identification and analysis of laser-induced damage.