<p>The evaluation of cap rock closure efficiency and the exploitation of natural gas significantly depend on the breakthrough pressure parameter. This experiment assesses the breakthrough pressures of CO₂ and CH₄ in partially saturated sandstone with low-permeability under various pressure and temperature conditions using a stepwise method. The novelty of this study lies in enhancing the understanding of the trends in CO₂/CH₄ breakthrough pressure under differing temperature and pressure conditions, as well as the comparative differences between them. Additionally, the study examines the effects of characteristics such as viscosity ratio, interfacial tension, and wettability on breakthrough pressure. The findings reveal a positive correlation between CO₂ breakthrough pressure and both pressure and temperature, while CH₄ breakthrough pressure exhibits a negative correlation with these variables. Under varying pressure and temperature scenarios, the breakthrough pressure of CO₂ surpasses that of CH₄, with both being more significantly influenced by the pressure conditions. Furthermore, CH₄ breakthrough pressure is more sensitive to changes in pressure or temperature compared to CO₂. Based on the displacement stabilization phase diagram, viscosity ratio and capillary force emerge as the dominant factors affecting the breakthrough processes of CO₂ and CH₄. This study provides valuable references for evaluating the sealing properties of caprock, offers guidance for CO₂-EGR engineering, and contributes to the establishment of numerical models for CO₂/CH₄ mixed gases.</p>