The invention provides a hydraulic folding formwork. The hydraulic folding formwork comprises two suspension girders, two formwork support frames, N sliding seats, locking devices, a formwork, an oil cylinder and a longitudinal moving mechanism. During pouring of concrete, equipment girders of the hydraulic folding formwork are locked and fixed on the sliding seats through the locking devices, and the oil cylinder drives the formwork to swing upwards; then a concrete bridge deck is poured on a steel box girder, a flange part of the concrete bridge deck is poured on the formwork, when pouring construction is finished and die opening is executed, the oil cylinder drives the formwork to rotate downwards to be separated from the flange of the concrete bridge deck, then the longitudinal moving mechanism pushes whole equipment to slide relative to the sliding seats to realize forward movement, and die spotting is performed after the equipment is in place and a new round of construction is performed. The whole construction process is just performed at the upper part of the bridge and synchronous with operation under the bridge, a support is not required to be constructed under the bridge, the construction process is simple and convenient and requires few constructors and machines, the construction efficiency is improved, the construction period is shortened, and the problems of cross construction on the bridge and under the bridge are solved.