To meet the degaussing service requirements, the phase lag of the eddy current magnetic field in conductors needs to be studied and calculated for better magnetic compensation of conductors. A method for calculating the phase lag angle of the eddy current magnetic field in the conductors has been proposed based on magnetic variation simulation method. Firstly, the calculation method of the phase lag angle of the eddy current magnetic field in the conductors is deducted theoretically. Subsequently, the external excitation magnetic field is applied in the conductor space by using the magnetic variation simulation method in the COMSOL software, and the simulation results are consistent with theoretical calculations with an average error of 0.025%. Finally, the eddy current magnetic field measurement experiment is carried out to validate the accuracy of the theoretical and simulation results, with an average error of 2.48%, satisfying engineering requirements. The simulation analysis and experimental validation therefore show that this approach enables rapid and precise calculations of the phase lag angle of the eddy current magnetic field at different frequencies, which can be used in practical engineering calculations.