Abstract: According to the relationship between CR transmission line model (CR circuit) and QR circuit,an approach to calculate the initial value for fitting the former was found. Then,accurate values of its all elements could be obtained by using Z-View software. Based on the distribution of capacitance (Ci) and resistance（Ri）vs characteristic frequency (f*),the function of the relative increment of its elements vs the CPE(constant phase element)－power n could be drawn out. It showed that Ci value increased more quickly than that of Ri when n < 0.5, so the physical meaning of n and its connection with the delamination at the coating/metal interface were interpreted from a new standpoint. As examples of application, the fit of several different types of electrochemical impedance spectroscopy, the inspection of the evolution of impedances in organic coating/metal system with time, discrimination of the effects of corrosion and delamination on the impedance,as well as the samultaneous estimation of capacitance and resistance of coating with various interspace from high impedance system were performed. Finally, the physical meaning of the CR circuit in organic coatings system was discussed for the heterogeneous characteristics of organic coating.

Key words: Electrochemical impedance spectroscopy (EIS), Transmission line, 　Physical meaning, Organic coating