The procedures of the methodology is as below: 1) The new cross-over superstructure unit shall first be hoisted with spreader and spliced to the front edge of bridge which has been completed and, if necessary, provided with temporary reinforcement and adjustment devices. 2) Use the front end of the upper structure unit which has been completed by the cantilever as a guiding device. Then implant the remote lower structural pier column into the soil to a predetermined depth. 3) Joint the lower structural pier column with the completed cross-over superstructure unit to build a new bridge. 4) The unit of superstructure shall be applied first and then the top-down construction method of the lower structure shall be applied. Cross-span construction until the bridge or viaduct is completed.