Stir casting process is the most important method in the aluminum matrix composites synthesis industry. In the stir casting process, the stability of the liquid aluminum surface and the highest shear force induced by the impellers are the two main factors for high quality of aluminum matrix composites synthesis. In this paper, a three-dimensional CFD model validated on a water and air two-phase flow system in a cold model was used to optimize the mixing string tank for aluminum matrix composites synthesis, coupling the volume of fluid (VOF) model, the k-E turbulence model, and the multiple reference frames (MRF) model. Important mixing parameters of the gas-liquid two-phase stirred tank such as rotation speed, type of baffles, and angle of rotating impellers were simulated and analyzed in detail. Varieties of speed were investigated to choose the best one. The best stirrer was chosen through analyzing the stability of liquid aluminum and shear force induced by impellers. The results showed that the optimal stirring speed was 180rpm during studying the surface between liquid and gas. The best baffles with the lowest vortex were obtained through simulation, with dimensions of 50mmx20mmx350mm. In order to get the lowest vortex between water and air and the strongest shear force, the blades should be installed at 15 degrees with vertical direction.