 It acts as an extension of X-ray computed tomography (CT) to a different waveband.It mainly studies the establishment of process models such as refraction, reflection and diffraction when terahertz waves transmit samples, which has certain requirements for reconstruction algorithms.According to the different transmission delay of Terahertz wave reflected signal at different depths inside the sample, the depth information can be obtained by processing the reflected signal inside the sample to realize the tomography.