Abstract: The construction of projects on remote islands and reefs faces severe challenges, including insufficient corrosion resistance of traditional building materials and high costs for long-distance marine transportation. The use of localized materials and composite materials represents a feasible solution, though the bonding performance between GFRP-steel composite bars and coral seawater sea-sand concrete remains unclear. To address this issue, this study designed five groups comprising a total of 15 central pull-out specimens to analyze the effects of coral seawater sea-sand concrete strength, GFRP-steel composite bar diameter, and bond length on bonding performance. Bond strength and basic anchorage length calculation formulas for GFRP-steel composite bars and coral seawater sea-sand concrete were proposed. The results indicate that the bond strength is primarily positively correlated with the cube compressive strength of CSSC and the bond length of GFRP-steel composite bars, while the initial bond stiffness shows a positive correlation with the cube compressive strength of CSSC. The experimental data can provide support for the application of localized materials in the construction of remote island and reef projects.