SiCp/Al-Mg metal matrix composites were manufactured by semi-solid stirring technique. The composites were remelted and then solidified under different pressures to study the solidification behavior of composites by differential thermal analysis, scanning electron microscopy, and transmission electron microscopy. The experimental results show that SiCp reinforcements can not act as heterogeneous nucleation sites for α(Al), and an interfacial layer composed of MgAl2O4 spinel and Si-rich phase existed at Al/SiCp interface. The undercooling of the matrix alloy was improved by the pressure applied, resulting in the grain of matrix alloy refining. The X-ray diffraction pattern of composites testified that the matrix alloy exhibited a certain preferred orientation during solidification. In addition, with increasing the pressure for solidification, the pored defects in the composites decreased, while the relative density, hardness and compressive strength increased. Therefore, the microstructure and mechanical properties of the composites were improved by pressure placed during the solidification of SiCp/Al-Mg composites. SiCp / Al-Mg metal matrix composites were manufactured by semi-solid stirring technique. The composites were remelted and then solidified under different strains to study the solidification behavior of composites by differential thermal analysis, scanning electron microscopy, and transmission electron microscopy. results show that SiCp reinforcements can not act as heterogeneous nucleation sites for α (Al), and an interfacial layer composed of MgAl2O4 spinel and Si-rich phase existed at Al / SiCp interface. The undercooling of the matrix alloys was improved by the pressure applied , in the grain of matrix alloy refining. The X-ray diffraction pattern of composites testified that the matrix alloy exhibits a certain preferred orientation during solidification. In addition, with increasing the pressure for solidification, the pored defects in the composites decreased, while the relative density, hardness and compressive strength increased. Therefore, the microstruc ture and mechanical properties of the composites were improved by pressure placed during the solidification of SiCp / Al-Mg composites.