Wire-arc sprayed Al-based composite coatings were commonly used for protecting offshore equipment, but the ceramic additions play a critical role in influencing the corrosion performance of the coatings. Consequently, the long-term immersion behavior of newly developed Al/Al2O3 composite coatings was investigated. Benefiting from the densification of cored wire by rotary swaging process, the most Al2O3 particles endured adequate melting and deformation during wire-arc spraying, thus obtaining a high deposition ratio and dense composite structure even when the addition content achieved 30 wt.%. All the composite coatings exhibited excellent corrosion resistance, reliably protecting steel substrates in 3.5 wt.% NaCl aqueous solution over 2160 h, due to the combination of cathodic protection and physical barrier. The corrosion process evolved undergo three stages, including localized pitting initiation, corrosion products accumulation, and dynamic equilibrium of the barrier layer. The Al2O3 addition displayed a positive effect on decreasing the corrosion rate of composite coatings by reducing the active area on the electrode surface. Simultaneously, the Al2O3 addition played a crucial role on promoting the stability of the barrier layer formed on composite coatings, whose underlying mechanism was disclosed to alleviate growth stress. The findings here experienced for future works aiming to formulate corrosion-resistant coatings served in marine environment. Graphic Abstract