Abstract: For the purpose of measuring thickness and conductivity of all the layers of three-layered plane conductors at one time, a forward problem model was built. In the model, analytic solution of an air-core cylindrical coil’s impedance caused by eddy current in three-layered plane conductors was presented. Calculated results based on the presented analytic solution agreed well with the experiment results. After this, an inverse problem was put forward. The ultimate goal was to calculate the thickness and conductivity of all the layers of three-layered plane conductors when the probe impedance caused by eddy current at several frequency points was acquired. Combined with the analytic expressions, optimization algorithm was employed to solve the inverse problem. Inversion results for the three-layered plane conductors showed that the proposed method was practicable and the accuracy was good.