Equivalent circuit modeling is a powerful technique for analyzing the complex impedance of polymer electrolyte membrane fuel cells. The transmission line model, which is based on reactant transport and electrochemical reactions, is frequently applied to porous electrodes. In this study, the distribution of the local charge transfer resistance was considered to accurately evaluate the dependence of the impedance on relative humidity (R.H.). The impedance of the prepared single cell was measured at 0.7 V under various R.H. conditions. The fitting results to the measured impedance spectra confirmed that a strong positive correlation exists between R.H. and proton conductivity. The exchange current density was determined in advance to simulate the impedance with dependence on R.H. The proposed model can simulate the experimental trend in which the total resistances of proton conduction and charge transfer decreased inversely to R.H.