SiC has long been the most widely recognised reinforcement for magnesium matrix composites (MgMC), yet the grain refinement mechanisms of SiC nanowhiskers (SiCnw) are still not fully understood. No direct observations of nanoparticles interacting with Mg dendrites have yet been documented. This study intends to conduct in-situ solidification experiments on MgMC using X-ray tomography at the ID19 beamline, observing the effects of SiCnw (diameter 650 nm, length 5 μm) on the nucleation and dendritic growth evolution of alpha-Mg grains. Subsequently, solidified samples will be scanned using diffraction contrast tomography (DCT) at the ID11 beamline to study the crystallographic orientation relationships between SiCnw, T2-Al2MgC2 phase and alpha-Mg. The experimental data will also be integrated with numerical simulations of grain growth, offering substantial insights into the study of the grain refining mechanism of SiCnw on Mg.