With the development of bimetal composite technology, copper-aluminum composites have shown certain advantages in many aspects. Therefore, this material has been used in various electric power equipment, such as wires and cables, transformers, and power distribution cabinets. However, some manufacturers replace copper by this alloy but do not inform the customer, which makes it difficult to operate and maintain the equipment. Therefore, there is a need for a rapid non-destructive testing method for conductor materials. Based on the theory of electromagnetic field, this paper establishes a mathematical model of AC resistance of copper-clad aluminum conductor. The variation AC resistance with frequency is simulated. With normalization of resistance under different frequency, we see that the resistance variation is different with different copper content. There is a corner point in the frequency responses. By comparing and analyzing the corner frequency, the non-destructive identification of windings with different materials can be realized. Then, the paper carries out experimental test based on the simulation model, which confirms the feasibility of the non-destructive testing technology of winding materials based on the resistance frequency response method.