Due to long exposure to nature, the Inscriptionless Stele of the Qianling Mausoleum has been suffering from serious weathering on its surface. Temperature is one of the main factors affecting it. In order to explore the distribution regularity of the Inscriptionless Stele temperature field, we constructed a 3D analytical model of the Inscriptionless Stele based on fundamental principles of heat transfer theory and then calculated its temperature distribution under solar radiation by using Comsol Multiphysics simulation software. The results show that the temperature variation tendency of the Inscriptionless Stele from the surface to the inside manifests itself as a parabola. The closer to the center of the Inscriptionless Stele, the smaller the daily temperature variation. Depending on sun’s azimuth and elevation angles, the temperature distribution on the four surfaces of the Inscriptionless Stele is extremely uneven. A temperature gradient occurs both horizontally and vertically. The results of this study can provide effective scientific evidence for the protection of the Inscriptionless Stele.