Geological storage of CO 2 in deep saline formations is increasingly seen as a viable strategy to reduce the release of greenhouse gases into the atmosphere. However, possible leakage of injected CO 2 from the storage formation through vertical pathways such as fractures, faults and abandoned wells is a huge challenge for CO 2 geological storage projects. Thus, the density-driven fluid flow as a process that can accelerate the phase change of injected CO 2 from supercritical phase into aqueous phase is receiving more and more attention. In this paper, we performed higher-resolution reactive transport simulations to investigate the possible density-driven fluid flow process under the 'real' condition of CO 2 injection and storage. Simulation results indicated that during CO 2 injection and geological storage in deep saline formations, the higher-density CO 2-saturated aqueous phase within the lower CO 2 gas plume migrates downward and moves horizontally along the bottom of the formation, and the higher-density fingers within the upper gas plume propagate downward. These density-driven fluid flow processes can significantly enhance the phase transition of injected CO 2 from supercritical phase into aqueous phase, consequently enhancing the effective storage capacity and long-term storage security of injected CO 2 in saline formations.