Based on Dongting Hu three-tower cable-stayed bridge on high-speed railway, stiffness ratio of middle tower to side tower (SROMTTST), vertical bending resistance stiffness (VBRS) of girder, height of tower, area of cable were studied by using FEM. The results show that the structure is more economical on condition of the SROMTTST less than 3.0. With the increase of VBRS of girder, the tensile forces of the cables near mid span increase and decrease near towers. Meanwhile, both the moments of the tower and the deflection of the girder get smaller. The ratio of tower height to span (ROTHTS) has great influence on the bridge rigidity. Every 0.01 increase of the ROTHTS can decrease a ratio of deflection to span (RODTS) about by 3%～5%.