The degradation coefficient is proposed to evaluate the degradation degree of organic coatings by directly analyzing the Bode plots of the electrochemical impedance spectroscopy (EIS) data.This paper investigated the degradation of phenolic epoxy coating/tinplate system by EIS and the degradation coefficient value,which correlates well with the results of breakpoint frequency and variation of phase angle at 10 Hz.Furthermore,the degradation process was confirmed by scanning electron microscope (SEM) and scanning probe microscopy (SPM).It is concluded that degradation coefficient can be used for the fast evaluation of degradation degree of organic coatings in practical applications.