In order to confirm that the Large Eddy Simulation(LES) is applicable to the study of aerodynamics of bridge girder, the wind field around a box girder of a large span cable-stayed bridge, under Reynolds number of Re=1.27×105 in uniform flow, was accomplished by using three-dimensional Computational Fluid Dynamics(CFD) analysis. The LES employes the Smagorinsky subgrid turbulent model. Based on the grid and time step size independent check, the averaged drag, lift and moment coefficients, as well as the Strouhal number at various angles of attack, were obtained. The research shows that the vortex shedding is not synchronous in span-wise direction, and its energy is concentrated to a band including several peaks. Based on the distribution of mean and root-mean-square value of pressure around the girder surface, the flow separation and reattachment pattern on the girder surface were presented, and the reasonable arrangement of pressure taps on wind tunnel models was suggested. The results were compared with the results from wind tunnel tests. It is confirmed that the LES is capable of investigating the aerodynamics of bridge girders and flow mechanism.