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 (CSSC) 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 CSSC 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 ultimate bond strength of test specimen 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.