A new method for ocean sequestration of low purity CO2 gas emitted from thermal power plants has been developed. The method utilizes a gas-lift pump system, named gas lift advanced dissolution (GLAD) system, that dissolves the CO2 (which has been separated from combustion gas) into seawater at a relatively shallow depth of 200-300 m and then transports CO2-rich seawater to a depth greater than 1000 m. The CO2 concentration of seawater after sequestration shall be limited to a certain value (e.g. 3 mol/m(3)) so as to minimize the impact on marine life. This paper describes the numerical simulation model of GLAD's two-phase flow with a CO2 dissolution that was used to determine the optimal specification of the system. This numerical simulation resulted in the following conclusions: 1 The required length for full dissolution in the dissolution pipes is proportional to the diameter of the injection bubble, and increases linearly with the decrease in the purity Of CO2 gas. 2 The allowable injection rate of CO2 gas, for a marine life, is proportional to the sectional area of dissolution pipe and increases with the increase in impurity (= 1 - purity) of the CO2 gas and the diameter of the injection bubble. 3 Analysis of correlations among these factors will enable system optimization on the total cost basis including the costs for CO2 separation from exhaust gas, transportation of CO2 gas to the GLAD site and CO2 sequestration.