In this study, the transport of chloride ions and oxygen in coral aggregate seawater concrete (CASC) was examined under realistic working conditions. The concrete specimens were subjected to pre-applied compressive strengths of 0%, 25%, 45%, and 65%. The diffusion coefficients of oxygen gas in the CASC were determined by different loads, and the diffusion of chloride ions was also analyzed. The concrete was subjected to continuous loads of 0%, 10%, and 20% of their maximum compressive strength and the chloride ion content was measured after being exposed to seawater erosion. The results showed that the diffusion of oxygen concentration follows the pattern of initial rapid and then gradual decline, the higher the load, the more microcracks are generated, resulting in a larger diffusion coefficient of oxygen. Chlorine ions and oxygen have similar diffusion patterns.