A cellular automaton-lattice Boltzmann (CA-LBM) model coupled with flow field, temperature field and solute field was established to simulate the grain formation process of aluminum alloy in the flow process. The influence of flow on crystal growth was simulated. The results show that the existence of convection makes the crystal no longer grow symmetrically under the condition of pure diffusion, the growth of dendritic crystals at the upstream side is promoted, and the growth of dendritic crystals at the downstream is inhibited due to solute aggregation; the greater the flow velocity , the stronger the asymmetry of dendrite; the higher the cooling rate, the higher the nucleation density and the number of nucleation, and the smaller the grain size; the larger the temperature gradient, the smaller the nucleation number and the larger the grain size; the greater the undercooling, the faster the dendrite growth, the coarsening of the dendrite arm, and the more developed the secondary dendrite growth, which caused the higher concentration of solute at the solid-liquid interface at the tip of the dendrite, and aggravated the solute segregation.