Abstract: In this study, the lattice Boltzmann method (LBM) is employed to investigate the flow and mixing behavior of miscible fluids in a lid-driven square cavity. The effects of the initial fraction of low-viscosity fluid, the viscosity ratio (M), the Péclet number (Pe), and the Reynolds number (Re) on the displacement and mixing processes are systematically examined. The results indicate that increasing either the initial fraction of low-viscosity fluid or the viscosity ratio M delays the stabilization of the flow field, while exerting minimal influence on the overall velocity and concentration distributions. A higher initial proportion of low-viscosity fluid or a larger viscosity ratio M results in a lower diffusion speed of concentration during mixing. Both Pe and Re significantly affect the flow and mixing: higher Pe or lower Re suppresses mixing but accelerates flow stabilization. Furthermore, under low Pe or relatively high Re conditions, the concentration field evolves from a typical triangular structure to a circularly symmetric pattern.