(Al₂O₃+Al₃Zr)p/A356 composites were synthesized by melt-reaction in A356-Zr（CO₃） system with electromagnetic stirring.Observation of solidified microstructure by SEM show that the volume fraction and dispersity of reinforced particulate with the size of 1～3 μm in matrix can be improved with the stirring intensity increasing due to the electromagnetic stirring promoting heat transfer and solute diffusion to improve in-situ synthesized kinetics.Meanwhile,co-action of electromagnetic stirring and in-situ particulate results in the transformation of Si phase from sheet primary Si to needle-like or fine-rod eutectic Si.