A Cu interconnect having a diffusion barrier formed with the self-formed high-entropy alloy a method of preparing the same are provided. A high-entropy alloy and Cu are deposited together. When annealing, a diffusion barrier is formed through segregation of the high-entropy alloy may, toward a bottom and a sidewall of an interconnect via, and a Cu seed layer is formed through segregation of Cu at an outer surface of the diffusion barrier, so as to simultaneously self-form the diffusion barrier formed with the self-formed high-entropy alloy and the Cu seed layer. The Cu interconnect having a diffusion barrier formed with the self-formed high-entropy alloy comprises: a base, the self-formed diffusion barrier formed with the self-formed high-entropy alloy and the Cu seed layer and a Cu electroplating layer electroplating on the Cu seed layer.