Dental caries are closely related to pulp infection status and vitality, and the depth of caries determines the clinical treatment. However, the detection and diagnosis methods of dentin caries, such as visual examination and probe, are easily affected by subjective factors. X-ray assistive examination for caries has low sensitivity and some defects, and its reliability and effectiveness still need to be improved. Terahertz time-domain spectroscopy can image different physical parameters, which has great potential in the physical and nondestructive detection of dentin caries. This study aimed to explore terahertz spectral images of dentin caries. Experiment by transmission and reflection type scanning terahertz platform, to 15 containing dentine caries in vitro teeth grinding slice scanning, through the data of two-dimensional reconstruction, won the terahertz transmission and reflection of different parameters in the image. Terahertz images and laboratory studies of dental decay light image and X-ray image contrast, the proposed merger under light microscopy, THz image caries damage area is under evaluation.The results show that the terahertz image is consistent with the light mirror image and has higher sensitivity than the X-ray image.Under the reflection mode, the sample thickness, surface roughness and system noise greatly influence the experimental results due to the weak THz reflection signal. The image can only identify the contour of the sample but cannot be used to distinguish enamel, dentin and dental caries.In the transmission mode, both the frequency domain 1.4 THz phase difference imaging and the time domain imaging corresponding to the minimum signal can be used to distinguish enamel, dentin and dental caries, and the time imaging corresponding to the minimum signal can be used to distinguish the three, among which the time imaging corresponding to the minimum signal has the best effect.Measured under the light dentine caries damage area and terahertz time-domain signal of transmission mode for the minimum time corresponding image of dentine caries damage area matching samples Wilcoxon signed-rank and inspection. The results (p>0.05) still cannot think of two methods in the area of dentine caries loss difference, two methods of measuring the difference due to system error.Therefore, we can think that the diagnostic information such as the range and size of dentin caries can be obtained through the time-image corresponding to the minimum value of time-domain signal in the terahertz transmission mode.This study shows that terahertz imaging technology can provide a more accurate and effective diagnostic method without ionizing radiation for the early diagnosis of dentin caries and provide some morphological basis for clinical digitalization and minimally invasive caries removal.