The method of strengthening the existing reinforced concrete suspension bridges by changing suspension system into cable – stayed- suspension system is presented in this paper. Based on a typical bridge, the analysis of the static behavior of the bridge before and after the strengthening is preformed. The results show that the bending moment of the girder is reduced obviously and the capacity of carrying load is greatly improved. The original cable system is fully utilized and can meet force requirement. It has certain theory significance and practical engineering value to the similar bridge’s strengthening.