In permafrost regions, the construction of highway would cause thawing of underlying permafrost, which threatens the stability of engineering. This frozen soil problem is important for the engineering construction in permafrost regions. For the Qinghai-Tibet Expressway, due to the asphalt-concrete pavement with high heat absorption and scale effect caused by large embankment width, the heat absorption of embankment will increase greatly, resulting in permafrost problem more severe. In this paper, through numerical simulation, taking into account of global warming, the thermal characteristics of large-width embankment after 20 years of completion of works are predicted and analyzed. The influence of large-width asphalt-concrete pavement on the thermal characteristics of underlying permafrost is investigated. Additionally, the underlying permafrost thermal characteristics are compared between large-width embankment and separated double line embankment. The study result would supply fundamental theory guide for the stability study and construction model of expressway in permafrost regions.