The marine atmospheric corrosion of Al-alloys could be originated from the localized corrosion beneath thin electrolyte layers. The pitting initiation of Al-alloy AA6061 beneath thin electrolyte layer of 3.5%NaCl and bulk solution, as well as the corrosion inhibition of cerium ions were comparatively investigated by means of polarization curves, electrochemical impedance, electrochemical noise and micro-morphological observation. Results demonstrate that, as a cathodic corrosion inhibitor, the density and coverage of the deposited CeO₂ film is mainly related to the thickness of thin electrolyte layer, the thinner the electrolyte layer is, the more compact the deposited CeO₂ film becomes. As a result, the oxygen reduction on the secondary intermetallic phase (Mg₂Si as cathode) of AA6061 alloy would be suppressed and therefore further refrain the initiation and development of pitting corrosion. The thinner the electrolyte layer, the higher the inhibition efficiency of cerium ions. Whereas, the inhibition efficiency of Ce³⁺ on the metastable pitting corrosion of AA6061 alloy in bulk NaCl solution decreases much more in the contrast to that beneath thin layer of NaCl solution.