CO2 geological storage technology is a crucial method for solving environmental problems, and long-term safety of the caprock is a crucial safeguard for CO2 storage project implementation. Fluctuation in caprock pressure during CO2 storage may lead to the creation of fractures and subsequently increasing the risk of caprock leakage. Determining the leakage risk is critical in order to ensure the integrity of the caprock during CO2 storage, and breakthrough pressure is the most effective and intuitive parameter for caprock safety evaluation. This research systematically discussed the influence of different proportions of sequestered gas on the breakthrough pressure of fractured caprock through step-by-step experiments. The experimental results demonstrate that the breakthrough pressure of the CH4 gas mixture was greater than that of the N2 gas mixture, and the breakthrough pressure decreased as the gas mixture's molar percentage of CO2 increased. As the fracture angle in the samples increases, the breakthrough pressure of mudstone samples first decreases and then increases, exhibiting a concave changing trend. This research may provide theoretical basis for the safe implementation of practical CO2 geological storage projects.