Taizhou Bridge is the first kilometer level threetower and twospan suspension bridge in the world. The three-dimensional fullbridge FEM (finite element method) model of the Taizhou Bridge and the random vehicle loading on the bridge finite element model by simplified vehicle load model are established. The vertical displacement and bending moment values are calculated to analyze the position of the maximum stress for the steel box girder under vehicle load. Then the critical position can be determined to carry out fatigue analysis for the steel box girder.