Research conclusions: It is believed that the requirements of structural function of the subgrade in permafrost region can be satisfied by making design of subgrade structure in accordance with the frozen condition of“enclosed system”，filling the active layer on the surface by unfrozen coarse materials and making design of the rest parts of the subgrade like ordinary subgrade，after the permafrost is treated in accordance with the geological conditions and ground temperature condition and upper limitation of permafrost is no longer lowering.