Based on Dongting Hu three-tower cable-stayed bridge on high-speed railway, different cable measures to improve structural rigidity were studied by using finite element method (FEM). The results show that it's effective to adopt stiffening cables between towers to improve the rigidity of the bridge. The ratio of deflection to span (RODTS) with level stiffening cables is the smallest and the total axial force of these level stiffening cables is the biggest compared to other two arrangement modes with inclined and level-inclined stiffening cables respectively. Over-lapped strengthening cables can effectively improve the rigidity of the bridge. The RODTS decrease with the increase of the number of the over-lapped strengthening cables. With the increase of the areas of the stay cables, the RODTS decrease approximately linearly.