Abstract: There is a broad application prospect for copper clad aluminum composite flat bars in the power industry due to the advantages of high electrical and thermal conductivity of copper, as well as the low cost and low density of aluminum.Copper clad aluminum flat bars were prepared by horizontal continuous casting technology. The effects of different annealing processes on the interface microstructure and properties of copper-aluminum composite flat bars were studied by optical microscope, scanning electron microscope and electron tensile testing machine. The results show that the diffusion of Cu/Al atoms is promoted and the thicknesses of diffusion layers increases with the increase of annealing temperature, which results in the formation of CuAl₂, CuAl, Cu₄ Al₃ and Cu₉ Al₄ at the interface layer. The tensile strength of copper clad aluminum composite flat bars is reduced by annealing treatment, while the plasticity and the interface bonding strength are improved.What’s more, the conductivity of copper-aluminum composite flat bars with a soft state is slightly higher than that with a hard state, and there is little difference of the conductivity for samples with different copper-aluminum volume ratios.