Abstract:The embankment with open crushed-stone side-slope is a main measure to cool the permafrost under the embankment of Qinghai—Tibet Railway. According to the air temperature and geological conditions of the Qinghai—Tibet Railway test section at Beiluhe,the changes of the temperature field,velocity field and heat flow of the embankment with open crushed-stone side-slope at Beiluhe have been studied to research the cooling effect in day and night,cold and warm seasons. The following results can be drawn. (1) This embankment takes on a certain cooling effect on the underlying permafrost at night in warm season,which is different from the traditional views. (2) It has heat shield effect due to the solar shading during warm season;and the released heat in cold season is larger than that absorbed heat during warm season according to the results of the computed heat flow,which is helpful in protecting permafrost and keeping the thermal stability of the railway embankment. (3) The main type of heat transfer of the crushed-stone side-slope is the forced convection according to the velocity characteristics shown in results. (4) The main mechanisms of the cooling effect of the embankment with crushed-stone side-slope are solar shading effect of the crushed-stone side-slope and the unbalanced forced convection heat transfer caused by differences of wind flow velocities in day and night,cold and warm seasons.