Based on an experimental project of a deeply buried coaxial double-pipe with a burial depth of 2539 m in Xi’an, Shaanxi Province, China, this study gave due consideration to the symmetry of a buried pipe structure, built a full-scale axisymmetric model for heat transfer inside and outside the coupled pipe, and verified the reliability of the model. The vertical initial temperature distribution, lithology, and thermophysical parameters of the surrounding ground of the buried pipe in the model came from the optical fiber temperature measurement of the vertical borehole wall, the interpretation of drilling data, and the experimental detection of drilling cores, respectively. This study discusses the variations in ground temperature and thermal effective radius with time in the 50-year service process of the buried pipe based upon the model, explored the heat transfer performance of the buried pipe under different constant heat transfer loads and inlet water temperatures, and analyzed the attenuation rules of its water temperature or heat transfer capacity in long-term service.