Abstract: CO2/N2 injection in heavy oil reservoirs has been demonstrated to enhance oil recovery (EOR) and facilitate CO2 capture, utilization, and storage (CCUS). Interfacial tension (IFT) is a crucial parameter for characterizing oil recovery, but it can be influenced by real-time changes in reservoir pressure and temperature during gas injection. The impact of the CO2/N2 ratio on the oil–gas IFT under varying temperature and pressure conditions remains unclear. Therefore, a systematic study was conducted to investigate the effects of multiple parameters on the oil–gas IFT during development processes, and a three-dimensional (3D) database and a regression model of IFT were established using experimental data. The results show that IFT is strongly correlated with density difference, moderately correlated with pressure and CO2 proportion, weakly correlated with saturates content and resin content, and nonlinearly correlated with temperature, aromatics content, and asphaltene content, respectively. Moreover, it has been observed that an increase in pressure or CO2 proportion can lead to a reduction in IFT. However, the impact of temperature changes on IFT varies across different pressure ranges. We introduce a new parameter, the equivalent interfacial tension pressure during temperature changes (EITP), to characterize this effect and discuss the reasons for the emergence of EITP, providing new insight into optimizing the CO2/N2 injection ratio in the reservoir. This study aims to reveal the advantages of oil–gas interface characteristics under the influence of multiple parameters in promoting low-carbon and efficient development of heavy oil reservoirs, and to explore the significance of CO2/N2 for enhancing heavy oil recovery.