Abstract: As a representative rock type of the ancient continental crustal basement, gneiss plays a crucial role in understanding the thermal structure and tectonic evolution of the lithosphere due to its thermal transport properties. In this study, the thermal conductivity (κ) and thermal diffusivity (D) of precambrian metamorphic basement gneiss from Dali, Yunnan, located at the southeastern margin of the Tibetan plateau, were simultaneously measured under high-temperature (300 ~ 1073 K) and high-pressure (1.0 ~ 3.0 GPa) conditions using the transient plane source technique for the first time. The experimental results show that both κ and D decrease with increasing temperature, revealing that the heat transfer mechanism of gneiss is phonon thermal conduction, where phonon scattering is the primary mechanism leading to the decrease in κ and D. When the temperature exceeds 950 K, the saturation effect of phonon scattering causes κ and D of gneiss to no longer decrease but tend to stabilize. Empirical fitting reveals a significant positive linear correlation between pressure and the thermal transport properties of gneiss, suggesting that pressure enhances thermal transport. Based on the experimental results, it is inferred that the middle to lower continental crust may exhibit a relatively uniform thermal conductivity (2.0 ± 0.3 W·m-1·K-1). A lithospheric thermal structure model constructed from the experimental data indicates that the Moho temperature in the study area (at 44 km depth) ranges from 1030 to 1210 K, and the lithospheric thickness ranges from 65 to 95 km, showing a pronounced thermal gradient. Furthermore, by integrating the temperature–depth relationship of the brittle–ductile transition zone, the focal depth of large earthquakes in this region is constrained to 11 ~ 23 km. These findings provide new thermodynamic constraints on the tectonic deformation mechanisms and seismic hazard assessment in the southeastern Tibetan plateau.