The analytical and numerical modeling of CO2 sequestration in deep saline aquifers having different rock and fluid properties was studied under diffusion and convection mechanisms. In a diffusion dominated system, an aquifer with 100 m thickness was saturated with CO2 after 10,000,000 years. It was much earlier in a convective dominant system. In the diffusion process, the dissolution of CO2 in aquifer increased with porosity increase; however, in a convection dominant process dissolution of CO2 in aquifer decreased with porosity increase. The increase in permeability accelerated the dissolution of CO2 in aquifer significantly, which was due to increasing velocity. The dissolution process in the aquifer was realized faster for the aquifers with lower dispersivity. The results of convective dominant mechanism in aquifers with 1 md and 10 md permeability values were close to that of the diffusion dominated system. For the aquifer having permeability higher than 10 md, the convection mechanism began to dominate gradually and it became a fully convection dominated system for 50 md and higher permeability values. These results were also verified with calculated Rayleigh numbers.