In this paper,the effects of mechanical vibration on the microstructure and mechanical properties of A356 aluminum alloy were experimentally investigated,and the mechanism of dendrite breaking under the action of mechanical vibration was explored.The results show that ( 1) mechanical vibration helps to effectively eliminate material's shrinkage hole and section crack during the squeeze casting,reduce or even eliminate the micro casting pores in aluminum alloy and refine the grain structure,thus resulting in more compact microstructure; ( 2) in the initial solidification stage of the squeeze casting,to a large extent,mechanical vibration can break the secondary dendrite arms and increase the nucleation rate of materials; ( 3) the Kirkword model is of higher accuracy which is proved by a comparison between the experimental and the theoretical results; and ( 4) as compared with the gravity casting and the squeeze casting without mechanical vibration,the casting with mechanical vibration significantly improves the mechanical properties of aluminum alloy and achieves higher tensile strength as well as more elongation.