Compared with the traditional die pressing, the isostatic warm compaction is a better way to obtain dense and homogeneous polymer bonded explosive(PBX). To provide a meso-level structure basis for the study of precise physical properties of PBX, three dimensional mesoscopic structure of the cylindrical sample formed by 2, 4, 6-triamino-1, 3, 5-trinitrobenzene(TATB) granules under isostatic warm pressing was studied by X-ray microtomography(X-μCT). The results reveal that TATB granules are still intact after warm pressing, and typically have polyhedral morphologies. There are high density layers between neighboring granules, and the maximum contact number of which is 12. An analysis of CT images shows that the axial size distributions of the compacted granules remain unchanged, whereas a decreasing trend of the radial density and pressure along the axial direction is observed. The CT values dispersion of different slices is larger than 1.15%, but the bulk density tends to be homogeneous. By analyzing the internal force chain distribution, we found an isotropic compression characteristic of compacted TATB granules under isostatic warm compaction. The particle contact number is counted based on mesoscopic particle contact angle, from which the morphology and arrangement of compacted particles have been confirmed to be isotropic, while the local particles subjected to shear-compression loading could also be detected.