As for structural beam of travelling bridge under reciprocate loads, at the bearing there will be a large change in stress of structure, while at the ends and midspan, the change of stress of structure will be simple. In this paper, based on the bearing features of travelling bridge structure, as well as features of steel-truss beam and steel box beam, a new composite structure, which is named as steel truss-steel truss box beam, is put forward. This new structure adopts steel box beam with truss inside at the bearings, and adopts steel truss beam at the midspan. Based on a certain engineering project, combined with ANSYS, according to a serious of sizes and structure styles, work of modeling, analysing and optimizing has been done in this paper. As calculating results showed, steel truss-steel truss box beam not only has higher bearing capacity, structural bearing capacity and a better wholeness, but also has a lower steel usage, which can provide references for similar composite structures' research in future.