The cable-stayed suspension bridge is a novel composite structure with great overall stiffness and the capacity to span a long distance, which has been proposed for the design of some extra long-span bridges. To take further research on mechanical properties and behavior of this type of structure, the proposed preliminary design of a cable-stayed suspension bridge with a main span of 1800m is analyzed. The three-dimensional nonlinear analysis method is used to investigate systematically the influence of various principal structural parameters on the static and dynamic behavior of bridges. These parameters include the rise-span ratio, the suspension-to-span ratio, the constraint condition of the stiffened girder, the number of auxiliary piers at side spans, the layout of suspension cables, and the elastic modulus of suspension cables. Meanwhile, the selection of the rational values of these parameters is discussed.