Abstract: On the interface of the Cu–Al composite plate from horizontal continuous casting, the eutectic microstructure layer thickness accounts for more than 90% of the total interface thickness, and the deformation in rolling forming plays an important role in the quality of the composite plate. The eutectic microstructure material on the interface of the Cu–Al composite plate was prepared by changing the cooling rate of ingot solidification and the deformation in hot compression was investigated. The results show that when the deformation temperature is over 300°C, the softening effect of dynamic recrystallization of α-Al is greater than the hardening effect, and uniform plastic deformation of eutectic microstructure is caused. The constitutive equation of flow stress in the eutectic microstructure layer was established by Arrhenius hyperbolic-sine mathematics model, providing a reliable theoretical basis for the deformation of the Cu–Al composite plate.