In order to investigate the temperature distribution of Qinghai-Tibet railway roadbed, based on the governing equations used to study forced convection for incompressible fluids porous media, the finite element formulae for heat convection in porous media are derived by using Galerkin’s method and taking air streamline function and temperature in porous media as basic variables. The temperature fields in October of the common ballast roadbed and the special ballast roadbed with crushed rock underlayer, constructed on July 15, have been analyzed and compared as they would have been used for 50 a under climatic and geological conditions on Qinghai-Tibet railway. The calculated results indicate that the common ballast roadbed will raise permafrost temperature under the roadbed base as well as lead to unsymmetrical temperature field distribution of roadbed and high temperature thawing zone under the sunny side, consequently it causes the permafrost roadbed thermal unstability. The special ballast roadbed with crushed rock interlayer will reduce permafrost temperature under the roadbed and provide cold energy for the roadbeds, also it can lead to symmetrical distribution of roadbed temperature field, which can eliminate the disasters that result in uneven settlement with longitudinal cracks within the roadbed. Therefore, it is highly recommended that the roadbed with crushed rock underlayer may be taken as Qinghai-Tibet railway embankment structure in high temperature permafrost regions so that permafrost embankment can be protected as possible as it should be.