Traumatic brain injury (TBI) caused by shock waves is one of the most common fatal and disabling diseases, and thus the early detection and classification of blast-induced TBI (bTBI) have important clinical significance. In this paper, based on the continuous terahertz wave imaging system, the brain tissues of rats with different degrees of bTBI are detected by the continuous-wave terahertz attenuated total reflection (CW THz-ATR) imaging system, and the THz images of these brain tissues of different levels of trauma are classified and identified by the support vector machine (SVM). The imaging results show that the detection of brain tissues with mild and moderate bTBI can be realized by the THz-ATR imaging technology. Moreover, the identification and classification of THz images of different levels of trauma by SVM can achieve the accuracy of 86.36%. This suggests that THz imaging technology has great potential for the early and precise detection and diagnosis of different degrees of bTBI.