Geological storage of CO2 has been viewed as an effective means of reducing CO2 emissions and mitigating the greenhouse effect. In the Taiwan area, the Western Taiwan Basin is suitable for million-ton-scale geological CO2 storage. Numerical methods were used in this study to investigate reservoir performance under various injection pressures. Three formations in the basin, the Chingshui Formation, Kueichulin Formation and Nanchunag Formation, were modeled. Three different injection pressures (1.3, 1.5 and 1.7 times the initial pressure) were considered. The simulation results show that the cumulative injected CO2 mass is proportional to the applied injection pressure and that the storage security increases over time. An annual injection rate of 5 Mt year–1 could be achieved by applying an injection pressure of 1.5 times the initial pressure at the injection well. The pressure accumulation in the system featured three stages. The over-pressurization effects associated with the injection in the system decrease, and the pressure in the system almost returns to the original pressure conditions after 50 years following cessation of injection. The CO2 gas plumes simulated in this study also suggest that the modeled injection scenarios are safe in terms of CO2 leakage from the vertical fault in this area.