Abstract: The molecular dinamics were employed to model the sintering process of Al-Silicon carbide (SiC) composite system, and the structure analysis and tensile process of sintered bulks containing SiC particles of different sizes were carefully investigated. By calculating the volume of aluminum and the volume of internal holes, it is found that the increase of SiC particle size can promote the compactness of the composites after sintering, but too small size increases the porosity and the pore size.Through the analysis of sintered atomic structure and quasi static stretching, it can be concluded that the increase of SiC particle size can improve the dislocation density, but the improvement of tensile strength can not be achieved stably, because the tensile strength of sintered composite mainly depends on the size of the largest hole.In this atomic scale, sintered bulk with good compactness and great mechanical property can be prepared when the size of reinforcement is close to metal particles.