The pressing process for RDX crystals was investigated with a cone-beam micro-focus computed tomography(μCT). The voids among the pressed RDX crystals, and their section pressing density and distribution were analyzed. Results show that the density of RDX crystals becomes more compact and uniform under 150 MPa, but some visible micro-gaps still exists inside the crystals. The distribution gradient of pressing density is very obvious at along the direction of pressure. Increasing the pressing pressure will be favorable to the uniform of the density distribution, but too high pressure will induce macro cracks. As a nondestructive test method, μCT shows a strong capability in the research of RDX crystals density distribution during pressing process. 