The effects of punch velocity on the microstructures and tensile properties of Mg2Sip/AM60B composite were investigated. In comparison, the tensile properties of the permanent mold casting of this composite were also analyzed. The results indicate that the punch velocity obviously influences the microstructure through changing the secondary solidification behaviors and semisolid deformation mechanisms. The variations of the microstructures and deformation mechanisms are responsible for the changes in tensile properties and fracture modes of the composites. The best comprehensive tensile properties of this composite are obtained under the punch velocity of 60 mm/s. The resulting ultimate tensile strength and elongation of the composite are found to be 198 MPa and 10.2%, respectively. The excellent tensile properties of the thixoforged composite are ascribed to the elimination of porosities and the work hardening.