The roadbeds in permafrost regions are mostly high-temperature frozen soils,which are highly susceptible to melting by engineering. The wide-area highways in permafrost regions have obvious heatcollecting effect,the increase of roadbed width will lead to aggravation of roadbed diseases. The stability of subgrade has become a key problem to be solved in the construction of Qinghai-Tibet road project. The composite roadbed which is composed of perforated ventilation ducts and crushed-rock layers is an active cooling measure. To study the cooling effect of wide highway and the influence of roadbed width on the cooling effect of roadbed,based on the characteristics of velocity filed of air flow in the crushed-rock layer and the ventilation duct as well as temperature field in heat transfer of porous media,adopting the two-phase physical field coupling relations,the numerical analysis on the temperature field of the composite roadbed with ventilated crashed rock layer of wide highway is carried out under sunny-shady slope boundaries and global warming condition to analyze the cooling effect of the roadbed after 10 years of construction. The result shows that (1) compared with the plain soil roadbed,the abovementioned composite roadbed forms a stable ice core on the lower side of the roadbed,the cooling effect on the wide highway is more significant,and the width has an obvious effect on the wind speed field and temperature field of the roadbed; (2) as the width increases,the wind speed in perforated ventilation duct decreases,the wind speed in crushed-rock layer increases,the growth rates of ice core area and its depth become slower,the stabilization time of roadbed becomes longer,and the cooling effect of the composite roadbed is gradually weakened; (3) when the roadbed width is greater than 32 m,the wind speed growth rate of crushed-rock layer is obviously slowed down,the growth rates of the low temperature area and the edge depth decrease,the roadbed stabilization time is prolonged,and the 0 ℃ line rise height is reduced.