Hot pressed Al-based composites of 15% SiC/2009A1 (volume fraction) were prepared by powder metallurgy method. The effect of the variation of Al powder sizes (13 μm, 32 μm) and temperatures (560^oC, 580^oC, 600^oC) on their microstructure and mechanical property was studied using optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and tensile tests. The results show that the composite prepared with small Al powders has higher strength and ductility than that prepared with large Al powders. The reason could be attributed to the following three aspects. First, large Al powders result in the uneven distribution of SiC particles in the matrix. Secondly, in the composites prepared with large Al powders, Cu and Mg spread unevenly and which then react with the extrinsic contaminants such as Fe and O, forming large-sized insoluble phases. Thirdly, in the composite prepared with large Al powders, the bonding between SiC particles and the aluminum matrix is weak, which is particularly obvious when the hot pressing temperature is low, resulting in debonding of SiC-Al interface during tensile tests. The fracture mechanism of the composites prepared with the two Al powders was analyzed. At all hot-pressing temperatures, the composites prepared with small Al powders are fractured due to the tearing of the Al-matrix and fracture of SiC partculates. However, for the composite prepared with large Al powders, SiC particles and aluminum matrix tend to debond when hot pressing at low temperature, while the interfacial bonding is improved with the increase of hot pressing temperature. When hot pressing at 580^oC, the mechanical properties of the composites are the best, especially for that withsmall Al powders. Correspondingly, the tensile strength and yield strength reach 556 MPa and 381 MPa respectively, and the elongation reaches 9.2%.