Influence of alloying element silicon on the thickness of interface diffusion, the recrystallized structures, the interface bonding strength, the microhardness of the matrix and interface for Cu/Al clod-rolling cladding in a heat treatment condition was investigated by measuring and observing the mechanical properties and microstructures of the composite interface. The results show that silicon is able to discourage the diffusion of Cu and Al atoms, control the growth of metallic compounds between Cu and Al, refine the grains and increase the microhardness of aluminium matrix. But silicon decreases the interface bonding strength at high heat treatment temperature for a long holding time.