Research conclusions: ( 1) With the pier － top longitudinal support scaffolding method，the cast － in － place of the superstructure crossing the bridge can be conducted with security and high quality and efficiency． ( 2) By making full use of the pier top and space under the flange plate of the box beam to support the longitudinal bars along with sectional steel cross beam，it can be as the support platform for the outside modeling and operation． ( 3) By making full use of the existing materials，the cost can cut and the construction period can be reduced．