The interfacial interactions among supercritical CO2 , mixed salt solutions, and rock might play a key role in CO2 sequestration in deep saline aquifers. Molecular dynamics simulations were performed to investigate both bulk and interfacial behaviors of the CO2+brine (NaCl + KCl and NaCl + CaCl2 ) systems with hydrophilic silica at 323 K, 90 bar, and a total salt content of 5.4 mol/kg. For the CO2+brine (single salt) systems, the salting-out effect on the dissolved CO2 followed the order: KCl < NaCl < CaCl2 . The interfacial tensions (IFTs) of these systems showed the same ordering. These results are in line with the order of the hydration energies of the cations. The computed IFTs of the CO2+brine (NaCl + CaCl2 ) systems are qualitatively consistent with experimental works. An important finding is that at low ionic strengths, the simulated IFTs of the CO2+brine (mixed salt) systems showed an almost linear dependence on the NaCl concentration. However, at high ionic strengths, the IFTs exhibited a non-linear relationship with NaCl concentration. Similar trends are also observed for our IFT results obtained from density gradient theory. Contact angles (CAs) of water in the CO2+brine (mixed salt)+silica systems are not much affected by the salt type and composition. Overall, the capillary pressure of the CO2+brine (mixed salt)+silica systems decreases with increasing NaCl concentration. These results can provide important insights into the capillary force, which acts to restrict the leakage of the stored CO2 through the cap rock.