In this paper, we report the Terahertz computer tomography(Terahertz-CT). Compared with the x ray computer tomography(XCT), more information could be extracted to process the image. Theoretically, Terahertz-CT could be used to map the complex refractive index distribution in target three-dimensional space. Therefore, it is possible to employ the principle of Terahertz-CT to classify the target inside a black box. This implies potential applications is security inspection and nondestructive examination.