In order to study the influences of structure parameters on the structure mechanical characteristics of long-span suspension bridge. The Shiduhe bridge in Hubei Province was taken as the background of this study, The influence on structure line shape and free vibration characteristics of suspension bridge with the change of structure parameters was studied. The results show that main cable stiffness not only has greater effect on the structure shape of long-span suspension bridge, it also has obvious impact on structure free vibration frequency, in addition, the torsion displacement of stiffening girder can be reduced effectively by adding central buckle, it improves structure bending and torsion stiffness significantly, central buckle also can improve free vibration frequency of structure and enhance structure dynamic stability, It shows that the influencing factors of structure static characteristics are restricted by rigidity of main cable, free vibration characteristics are affected by main cable and central buckle, they are not very sensitive to the variations of the parameters of suspender cable, stiffening girder and main tower.