Abstract: In the marine environment far away from the mainland, the coral sand foundation can be improved by injecting the cement grout with a very small amount of graphene oxide (GO) through grouting or mixing piles and other processes, which can greatly increase the stone body’s ability to block chloride ion penetration. Based on the comparative analysis of the difference in the particle morphology of river sand and coral sand and changes in hydration products and microstructure before and after GO incorporation, this study employed a rapid chloride ion migration test, scanning electron microscope experiment, and Image-Pro Plus image processing to reveal the mechanism of the modified coral sand cement stone body blocking permeation by chloride. The result reveals that high particle angles, irregular shapes, and porous and internal pores are the main reasons for the lower coral sand cement stone body than the river sand cement stone body in blocking chloride ion permeability under the same process conditions. After mixing 0.02% (mass fraction) GO, 28 d and 56 d coral sand cement stones have the highest degree of improvement in blocking chloride ion permeability (39.43% and 48.93%) and are similar to those of ordinary river sand cement stones without GO addition under the same process conditions. The coral sand cement stone body’s antichloride ion penetration performance improvement is related to the amount of GO. The two are first positively correlated and then negatively correlated. 0.02% is the best mix-up measure after the experiment in the assay. Regulating cement hydration products to form a regular and orderly hydrated crystal shape, improving the morphology of the interface transition zone, filling the space of internal cracks, and repairing the morphological characteristics of the pores are the main reasons that allow the incorporation of GO to affect the resistance of coral sand cement stones to chloride ion permeability.