The SiC/Cu composite was prepared by the method, which is patented in China, casting the metal into the SiC skeleton in a special furnace at 1160°C by pressure, caused by pressure difference between pressured gas and vacuum. During the preparation, the SiC decomposed. The carbon precipitated and the silicon, which has well affinity with the metal, formed silicon-copper compounds as Cu4Si, gathering in the silicon-copper interface area, identified by means of EDS and XRD. The mechanism of the solid reaction was discussed and the microstructure and morphology was studied by means of optical devices, SEM, EDS and XRD as well. And the diffusion coefficient was calculated.