The microstructural structures of SiCp/AZ61magnesium matrix composite were studied in three different casting processes, and their hardness was measured. The results indicated that SiCp/AZ61 composites fabricated in stirring melt casting process, compared to those in fully liquid stirring casting process and in semi-solid stirring casting process, possessed fairly uniform distribution of SiC particulates and few porosity rate. It was an ideal metal matrix composites fabricated process. The Vickers hardness of non-reinforcement AZ61 magnesium alloy is higher than that of semi-solid billet, and the Vickers hardness of SiCp/AZ61 composite is obviously higher than that of the matrix. In the meantime, the Vickers hardness of SiCp/AZ61 composite can be continuously enhanced with an increasing of volume fraction of SiC particles.