Understanding the phase behavior and formation kinetics of CO2 hydrate is essential for developing the sequestration process of CO2 into the deep ocean and its feasibility. Three-phase equilibria of solid hydrate, liquid water, and vapor were determined for aqueous mixtures containing CO2 and NaCl/clay to examine the effect of both ocean electrolytes and sediments on hydrate stability. Due to the capillary effect by clay pores and inhibition effect by NaCl the corresponding hydrate formation pressure appeared to be a little higher than that required for simple and pure hydrate at specified temperature. In addition, the hydrate formation kinetics of carbon dioxide in pure water and aqueous NaCl solutions with or without clay mineral were also measured at various conditions. The formation kinetic behavior was found to be strongly influenced by pressure, temperature and electrolyte concentration. A simplified kinetic model having two adjustable parameters was proposed and the estimated results agreed well with the experimental data.