In-situ （Al2O3+Al3Zr）p/A356 composites were synthesized by direct melting reaction combining with high intensity ultrasonic. The microstructure and properties of synthesized composites were investigated by XRD（X-ray diffraction） and SEM （scanning electron microscope）. It is found that the reinforcements Al2O3 and Al3Zr with average size of 1μm can be observed in the matrix alloy

which is uniformly distributed into the composites. Eutectic Si phase in A356 alloy can be broken into Si particle by high intensity ultrasonic

exhibiting great refinement effects. The tensile strength of ultrasonic treated composites reaches up to 381.4 MPa

which is increased by about 20% compared with that of ones without treated by high intensity ultrasonic.