Abstract: The dendrite growth of binary alloy Al-Si under the forced convection was simulated by the phase field model coupled with the solute field and flow field. The influences of the forced convection on the morphology of the dendrite growth, the distribution, diffusion layer and micro-segregation of the solute, etc. were studied. The results show that the morphology of the dendrite growth, the distribution, diffusion layer and micro-segregation of the solute were significantly changed under forced convection. With increasing of the convection speed, the growth of the dendrite is asymmetric. The upstream dendrite growth rate is greater than that of the downstream. The secondary dendrite at upstream was more developed and the dendrite in normal direction was bias more serious to the upstream. In the upstream, the concentration gradient at dendrite tip frontier increases and the thickness of the solute diffusion layer decreases. On the contrary, the concentration gradient decreases in the downstream and the thickness of the solute diffusion layer increases. Furthermore, micro segregation of the dendrite also becomes more serious caused by the effect of convection. The simulation results are consistent with solidification theory.