Terahertz (THz) non-destructive testing technology has the advantages of non-destructive, non-ionizing and non-contact, and has been rapidly developed and applied in the non-destructive testing of fiber-reinforced composite materials in the aeronautics and astronautics field. In this paper, PTFE was inserted into 4 different depths (0.225 mm, 0.450 mm, 0.675 mm, 0.900 mm) of carbon fiber composite laminates as artificial defects, and the terahertz time-domain spectroscopy and imaging system was used to image and spectrally analyze it, discuss the imaging effects and spectral properties of defects under terahertz radiation. The results of the study show that in the frequency band of 0.25 ~ 2.0 THz, terahertz reflection imaging can successfully detect different depths defects in carbon fiber composites, the terahertz frequency imaging signal and spectral signal linear increased with the defect depth increment, the absorption coefficient imaging signal and spectral signal linear decreased with the defect depth increment, and with the increase of frequency, the power spectral density of the defect firstly increment and then decrement, and the absorption coefficient slowly increases. The results can provide a reference for the visualization and quantitative analysis of unknown depth defects in carbon fiber composites.