<p>A 3D numerical model coupling the volume of fluid (VOF) and discrete phase model (DPM) has been established to investigate the transport, dispersion, and deposition of nanoparticles (NPs) in molten steel. A modified VOF-DPM model integrating a Brownian motion formulation and electromagnetic field effects has been developed through a user definition function to precisely characterize NP dynamic and spatial distribution in molten steel. The results show that Brownian motion effectively promotes the transition of NPs from the tendency to deposit along the bottom and wall under turbulent conditions toward a more uniform distribution, increasing the horizontal dispersion rate (<i>D</i>_H) to 21.3% and reducing the bottom deposition rate by 12.8%. The application of an electromagnetic field markedly affects NP transport and spatial distribution in molten steel by regulating the flow structure. Under the rotating magnetic field, the induced secondary flow directs the NPs along distinct trajectories, resulting in a characteristic “central–bottom” enrichment pattern. Conversely, the traveling magnetic field establishes a pronounced unidirectional circulation that enhances the NP suspension and promotes spatial uniformity, achieving a 6.87% reduction in the deposition rate. Additionally, this uniformity enhancement exhibits a clear dependence on magnetic flux density, reaching an optimum at 0.08&#xa0;T.</p>