Abstract: Chloride ion is one of the major factor affecting the durability of concrete in marine environments. The paper employs a combination of experimental and mesoscale analysis to investigate the transport mechanisms of chloride ions in fully recycled coarse aggregate concrete. Four types of recycled concrete with varying recycled coarse aggregate contents were experimentally investigated using chloride salt dry-wet cycling tests. Subsequent to these tests, a mesoscale analytical model of chloride transport was developed through a secondary software development. The favorable correlation between the test and simulation results confirmed the viability of the model. Subsequently, the impact of critical factors, such as the thickness of the old mortar and the volume of recycled aggregate, on chloride ion diffusion performance was investigated. Although an increase in the thickness of old mortar accelerated the diffusion of chloride ions, but this effect was not significant. In contrast, a higher volume fraction of recycled coarse aggregate significantly enhanced the diffusion of chloride ions in the recycled concrete. Furthermore, the stochastic convex polygonal aggregate model proposed in this paper demonstrated stable performance in simulating chloride ion diffusion.