In recent years, terahertz (THz) imaging technology has received increased attention owing to the promising imaging tools now available for nondestructive testing. However, theoretical models of THz imaging systems are yet to be developed. In this study, we proposed a comprehensive mathematical modeling and simulation theory for the THz imaging system. Gaussian beam distribution was used in the mathematical modeling of the point spread function (PSF). The target function was convolved using the PSF, and the analog transmission of THz images was realized. The PSF of the imaging system was calculated using the optical imaging method. Next, the image was deconvolution-enhanced using the PSF. The image restoration results revealed that the image resolution improved. The restored image contains more details.