Abstract: The transverse compaction of textile composite preforms represents a critical deformation mode occurring during composite forming and manufacturing processes. Compaction induces alterations in the preform's micro-scale architecture and fiber volume fraction, thereby influencing the mechanical properties of final composite materials. This study conducted transverse compaction experiments on seven carbon fiber 3D woven preforms with distinct structural parameters. Micro-computed tomography (Micro-CT) technology was employed to comparatively analyze microstructural evolution before and after compaction, elucidating the influence of structural parameters on compaction deformation behavior. The results revealed that: Preforms with higher numbers of structural interlacing points, increased yarn layer counts, and elevated warp yarn density exhibited greater peak compaction pressures; The load decay during the holding stage demonstrated correlation with both peak pressure and fiber gaps - higher peak pressures combined with larger inter-fiber gaps resulted in more pronounced stress relaxation during the holding phase.