Shear-induced particle migration in the internal die flows of concentrated particulate suspensions during slot coating processes was investigated using a diffusive flux model implemented within three-dimensional computational fluid dynamics simulations. Comparative simulations demonstrated that particle migration markedly altered the internal flow characteristics and particle distributions inside the slot dies. Inhomogeneous particle distributions at the feed inlet were found to modify the flow behavior in the chamber region and profoundly affect the velocity and particle concentration fields in the slit region. These changes critically influenced the die exit velocity and concentration profiles, which governed the uniformity of the wet coating thickness. The insights obtained from this study offer practical guidance for die design and process control to achieve a uniform coating thickness and stable slot coating operation.