Aiming at the problem of judging the state of AC electric arc furnace under different working conditions, this paper deduces the time-varying resistance of AC electric arc furnace based on the energy balance relationship, superimposes the classical non-linear resistance model, innovatively adds the arc length random change model, and forms a new time-varying resistance model which can simulate the different working conditions of the electric arc furnace. The accuracy of the model is verified by simulation with MATLAB/simulink software. Then, the voltage and current of the simulated arc furnace in the melting and refining periods are decomposed by the ensemble empirical mode decomposition (EEMD) method, and the interharmonic characteristics of the arc furnace in different periods are obtained. The experimental results show that EEMD can eliminate the mode aliasing problem encountered by empirical mode decomposition (EMD), and ensure the accuracy and validity of the extracted voltage and current intermediate harmonic information. Based on this result, a method of judging the state of electric arc furnace according to the characteristics of Interharmonics under different working conditions is proposed.