On the basis of the existing theories such as permafrost, thermodynamics and fluid mechanics, as well as the climate features on the Qinghai-Tibet Plateau and the data collected from both laboratory and the on-the-spot test, this paper puts forward a set of analytical methods and a numerical module for ground thermal regime with consideration of engineering surface features and various natural elements such as wind speed, radiation, evaporation. This paper also probes into the defining method for physical thermal parameter of the silty clay and gravelly sand soil, which widely pervades on the Qinghai-Tibet Plateau. The numerical analysis indicates that the ground thermal regime is a comprehensive reflection of various external elements. It is suggested that the variation of external elements should be fully taken into consideration in engineering design. Furthermore, the analysis of the frozen soil subgrade indicates that the transverse thermal difference in subgrade, which affects the subgrade stability, is caused by transverse difference in external elements along the subgrade surface.