Abstract：From the governing equations used to study forced convection for incompressible fluids porous media，the detailed finite element formulae for heat convection in porous media are achieved by using Galerkin's method to solve the computational problem of temperature fields on the ripped-rock revetment roadbed in Qinghai—Tibet railway. The temperature change of the ripped-rock revetment roadbed and common ballast roadbed with north and south slopes，when their temperature difference is 1.8 ℃，are discussed and compared. It is found that the common ballast roadbed makes the temperature field unsymmetrically distributed，and provides heat energy for the foundation soil. In contrast，the ripped-rock revetment roadbed is able to ensure symmetrical temperature field distribution. At the same time，it continuously provides more energy for the roadbed and foundation soil，and 0 ℃ isotherm far above the native ground surface，which guarantees the active layer (frost-susceptible sub-clay) to be completely frozen during summer-time (on Jul. 15 and Oct. 15)，not to mention，i. e.，winter-time (on Jan. 15). Therefore，it is highly recommended that the ripped-rock revetment roadbed，the common ballast roadbed with the ripped-rock of 10 cm diameter，80 and 160 cm thick，paved on the south and north side slopes，respectively，be adopted as a kind of roadbed structure of Qinghai—Tibet railway with north and south slopes in permafrost regions as it can lead to symmetrical distribution of roadbed temperature field and raise permafrost table greatly with frost-susceptible sub-clay，the active layer before roadbed construction，completely frozen under the roadbed around the year，and then eliminate the disasters that result in uneven settlement with longitudinal cracks within the roadbed.
