Abstract: Silicon carbide particle (SiC_P) preforms with the particles sizes of 20 μm, 50 μm, 100 μm and 150 μm were prepared by compression mold forming and sinter process. High resolution (~1.0 μm) 3D X-ray micro-computed tomography combined with 3D pore-network models was used to study the effect of SiC_P particle size on the 3D morphologies and spatial structures of pores in the SiC_P preforms. The results show that the increase of the SiC_P particle size reduces the gap expansions caused by the starch decomposition and enlarges the interval voids among the packed particles. As the SiC_P particle size increasing from 20 μm to 100 μm, the pore shapes in the preform sections become more irregular, and hence the average area porosity of pores decreases as well as the spatial volume distribution homogeneity and the connectivity of pores become worse. In the pore-networks, the average effective sizes of both pores and throats increases, whereas the number of small pores or throats and the average pore coordination number decrease. When the SiC_P particle size reaches up to 150 μm, the larger gaps can be filled by more small particles and the pore spaces are segmented by the residual netlike binders on the particles surface, so that the spatial distribution homogeneity of pore volumes and the connectivity decrease significantly. Therefore in the pore-networks, the number of small pores or throats and the average pore coordination number increase.