The explosion limit serves as a key parameter for assessing explosion risks and prevention strategies of combustible gases. Through a self-developed 5-liter experimental platform for flammable gas explosion characteristics, the upper explosive limits (UELs) of CH₄/C₂H₆ and C₂H₆/H₂O gas mixtures under high-temperature and high-pressure conditions were investigated, revealing the influence mechanisms of methane blending ratios and steam concentrations on the UELs of ethane under such extreme environments. The results demonstrate that methane blending ratios (0−0.5) exhibit minimal influence on the UELs of CH₄/C₂H₆ mixtures at 200 ℃ and 0.4−0.6 MPa, and the UELs of CH₄/C₂H₆ mixtures increase with increasing initial pressure, while exhibiting a progressively diminishing rate of UEL increment. Under identical thermal conditions (200 ℃, 0.4−0.6 MPa), the UELs of C₂H₆/H₂O mixtures decrease approximately linearly with increasing water vapor concentrations (0−40%). Conversely, higher initial pressures enhance the UELs of C₂H₆/H₂O mixtures. Notably, under 0.5 MPa pressure, as temperature increases from 200 ℃ to 270 ℃, the UELs of both pure ethane and C₂H₆/H₂O mixtures containing 40% water vapor increase with a rise in temperature, with pure ethane demonstrating an accelerating UEL increase rate.