Based on the Runyang Yangtze River Highway Bridge, which consiss of one cable-stayed bridge of South Branch and one suspension bridge of North Branch, the three-dimensional overall bridge model was established using the FEM numerical simulation to analyze the bridge deformation and mechanical performance. And a global-local analysis method was proposed to study the mechanical properties of surfacing. The shape of suspension bridge has large effects on the mechanical performances of the surfacing. The tensile stress obtained in this paper is significantly bigger than those by the traditional model. For the central section of the cable-stayed bridge, the mechanical indexes values of the surfacing obtained by this method are little bigger than those by the traditional model; otherwise, for the other sections of the main girder that undertake the horizontal component compression of the cable, the tensile stress values of the surfacing are little smaller than those by the traditional model.