Combined support for arch-to-ring arch reinforcement construction of river-crossing bridge and erecting method of combined support

The embodiment of the invention relates to a combined support for reinforcing construction of an arch ring and an arch of a river-crossing bridge and an erecting method. The combined support comprises a plurality of sets of longitudinal stress distribution beams, a middle supporting structure and a plurality of transverse stress distribution beams, wherein the two ends of the longitudinal stress distribution beams are erected on the two abutment foundations below the arch ring respectively, the middle supporting structure is used for supporting the middles of the sets of longitudinal stress distribution beams, and the transverse stress distribution beams are laid on the sets of longitudinal stress distribution beams at the same time. The all-round scaffolds are erected on the transverse stress distribution beams; the ends, located on the same side, of all the transverse stress distribution beams extend out of the same closest set of longitudinal stress distribution beams by a distance not smaller than a prese