Combination of transmission electron microscopy and computed tomography (TEM-CT) is a powerful technique to characterize three-dimensional nature of materials. In this paper, its principle and application are described in detail. In addition, as an example, TEM and TEM-CT was applied on TiN-Ag nanocomposite synthesized by dc arc-plasma method. Microstructures of TiN-Ag nanocomposite were carefully characterized by TEM, and nano-morphologies by TEM-CT. It was found that the surface of nanocrystalline TiN matrix was covered by finely dispersed Ag nanoparticles, and it was found that they were physically attached but not chemically bonded. From these experimental results, formation mechanisms are also predicted.