This paper investigates fatigue durability of FRP-steel double-lap shear bonded structure in seawater environment. Three simulated environments (original-salinity seawater dry-wet cycle, triple-salinity seawater dry-wet cycle, and triple-salinity seawater immersion) with 30-, 60-, and 90-day maintenance duration are tested. Experimental results indicate that both the quasit-static and fatigue strength are degraded by the seawater maintenance, and longer maintenance will lead to continued deterioration of the bonded joints. The failure/damage of bonded joints primarily originates from the bonding failure in the docking zone and extend towards the two ends. For a specific bonded joint, the load amplitude (∆F) and cycle number (N) can be approximated fitted by a linear logarithmic curve. Based on this observation, a prediction model of the cycle number (N) for the bonded joints is proposed, and comparison demonstrated that the prediction model can effectively assess the fatigue strength of GFRP-steel double-lap shear bonded joints after seawater maintenance. The findings of this study can offer both theoretical and experimental foundations for assessing the durability of FRP-steel bonded structures in seawater corrosion environments.