SiC_P/Al alloy is one of most competitive particle reinforced metal matrix composite materials. For the SiC_P/Al alloy composites that volume fraction is lower than 25%, the mechanical properties were well known since many researcher worked hard in recent years. But when the volume fraction is higher than 35%, the mechanical properties of SiC_P/Al alloy were not understood so well. In this paper, the tension properties were tested for the high volume fraction (55%) SiC_P/Al alloy composites, the stress~strain curve showed obvious nonlinear properties. Macroscopic and microscopic fractography indicated that the fracture section of high volume fraction SiC_P/Al alloy looks flat like traditional brittle materials, the shape of SiC particle was irregular and with sharp angle, some micro--defects such as void, crack and interface debonding exist inside the materials. A cell volume element model of polygonal prism with sharp angle at both ends was developed to simulate the mechanical behavior of high volume fraction. This model could simulate the irregular shape and uneven distribution of the SiC particle. Furthermore, the volume element cell and multi--particles combined cell with defects were built to consider the effect of the void and interface debonding. The analysis results showed that the interface debonding was the most important cause of the nonlinear mechanical behavior of high volume fraction SiC_P/Al alloy composites.