Abstract: The experiments were performed on tensile,compressive and flexible properties of high volume fraction SiC_P/Al composites. The result indicates that the composites have no obvious linear yield process. Loading and unloading experiments were carried out . It is found that the macroscopic properties of this SiC_P/Al composite are similar to plasticity of metal materials under external load. It has a quantity of residual strain on unloading,and the reloading course is approximately the same as the last unloading course. The residual strain caused by tension is greater than that by compression. The material has a stable tangent modulus with the best potential of residual plastic formation under three-point bending. From the analysis on SEM fractography , it shows that the local and gradual microyields of nonhomogeneous distribution of the matrix are the main reasons that get the behavior of high volume fraction SiC_P/Al composites similar to that of plastic materials in macroscope. The residual stress in the process and microdefects in the matrix make the residual strain by tension greater than that by compression.