Carbon fiber reinforced epoxy and nylon were measured by means of potentiodynamic polarization, potentiostatic polarization and AC electrochemical impedance spectroscopy (EIS) in a solution containing 0.9wt% NaCl, 0.1wt% CaCl2 and 0.075wt% NaHCO3. Their microstructures were examined by SEM. The results showed that these two types of carbon fiber reinforced polymers (CFRPs) were electrically conductive and electrochemically noble, and exhibited different EIS characteristics. Strong anodic and cathodic polarization could damage their surface polymer layers. Based on their different microstructures and electrochemical behaviors, a surface polymer layer model was proposed for these CFRPs. (C) The Author(s) 2018. Published by ECS.