<p>This study develops a two-phase lattice Boltzmann model (LBM) to investigate the multiphysics coupling behavior of TiC/Ti6Al4V metal matrix nanocomposites (MMNCs) subjected to a moving annular laser heat source. The model integrates nanoparticle–fluid interactions and heat transfer to elucidate the influence of nanoparticles on molten pool. An innovative formulation is proposed for calculating the nanoparticle-induced dynamic viscosity, while an improved estimation method is adopted for the surface tension coefficient; moreover, a local nanoparticle volume fraction model is introduced to enhance the spatial accuracy of particle–melt interaction representation. The simulation results reveal that the annular laser generates a characteristic saddle-shaped molten pool, where the rear zone exhibits enhanced depth due to localized heat accumulation and convective recirculation. Incorporating TiC nanoparticles increases the melt zone (MZ) size while suppressing the heat-affected zone (HAZ), attributed to interfacial thermal resistance and viscosity-induced flow retardation. Force analysis indicates that the drag force dominates nanoparticle motion, whereas the thermophoretic force—though weaker—plays a crucial role in modulating migration near regions of steep temperature gradients. Nanoparticles exhibit a pronounced tendency to accumulate on the lateral sides of the laser-irradiated region, governed by the stronger drag force and weakened thermophoretic drive in these peripheral zones relative to the low-drag, high-thermophoresis core. These findings provide a fundamental understanding of particle–melt interactions under annular laser irradiation and establish a theoretical framework for optimizing process parameters in additive manufacturing of nanoparticle-reinforced metal composites.</p>