In this work, an A356 Al alloy based composite reinforced by core-shell structured (CS) particulates was prepared by powder thixoforming, and then further improved the comprehensive mechanical properties of the composite by T6 heat treatment. The results show that the CS particulates not only improved the ultimate tensile strength and yield strength of the composite (increased by 18.0% and 32.7%, respectively), but also rendered the composite an excellent elongation of 12% equivalent to that of the A356 alloy (10.8% and 11.3%, respectively). During the T6 heat treatment, the strength and hardness of the composite increased firstly (1-7h, i.e., under-aging) and then decreased (9-12h, i.e., over-aging) with the extension of the aging time, reaching the maximum value at 8h (i.e., peak aging). The ultimate tensile strength, yield strength and hardness of the composite at peak aging were 325.4 MPa, 254.4 MPa and 104.0 HV, respectively, which were 33.7%, 74.0% and 48.5% higher than those without the heat treatment, and the elongation was 9.4%, which was almost no decrease compared with that without heat treatment. In other words, after the T6 heat treatment, the CS particulates can improve the strength of the composite while retaining its good plasticity. Finally, the strengthening mechanisms of the composite are discussed by analyzing the size, density and type of the precipitates in the matrix of the composites aged for 8h and 12h.