Geological carbon dioxide (CO2) storage offers a cost-effective solution for reducing CO2 emissions and mitigating climate change. However, the injection of CO2 into a reservoir can cause an increase in pore pressure, leading to fault reactivation or detrimental changes in the caprock. These changes can hinder the sequestration of injected CO2, especially when it comes to CO2 leakage through the caprock, including capillary leakage, hydraulic rupture, and leakage along pre-existing faults. Therefore, evaluating the confinement capability of the caprock is crucial for accurately predicting the long-term safety and stability of CO2 geological storage. One of the most essential parameters for characterizing the confinement capability of the caprock is the CO2 breakthrough pressure. It represents the minimum capillary pressure needed for the non-wetting phase to replace the wetting phase and establish a dominant seepage channel through the caprock. In this study, we conducted the stepwise method to determine the CO2 breakthrough pressure at the core scale. Additionally, we investigated how different factors such as caprock lithology, caprock thickness, and burial depth affect this pressure. The results of the experiments indicate that: 1) the permeability of the caprock is inversely proportional to the breakthrough pressure, meaning the lower the permeability, the higher the breakthrough pressure; 2) the CO2 breakthrough pressure increases nonlinearly with increasing caprock thickness; 3) burial depth has a significant impact on the CO2 breakthrough pressure, which increases as the depth of burial increases. These findings provide a theoretical foundation for ensuring the safe and effective long-term stability of CO2 geological storage.