The microstructure and wear resistance of in-situ Mg2Si/Al-Si were studied in the different content of Sb. The result shows that when the content of Sb is 0.4%, the refining effect of primary Mg2Si granules in Mg2Si/Al-Si composite is best. The shape of Mg2Si turned into fine and even granules compared to the shape of Chinese character or treelike crystal before modification. At the same, the composite shows the best wear resistance and the loss of wear quality was reduced by 19%～37%. The improvement of the wear resistance by alloy elements is related to the modification of the Mg2Si granules and enhancement of the matrix. The main wear mechanism of in-situ Mg2Si/Al-Si composite is grain-abrasion.