The invention discloses an adjustable straining beam construction formwork based on pile foundations. The adjustable straining beam construction formwork based on the pile foundations comprises two groups of supporting frames, two carrying pole beams and two formwork main beams, wherein the two groups of supporting beams are fixed to steel reinforcement cages of a pair of bridge pile foundations correspondingly and are located at the same height, the two carrying pile beams are erected on the two groups of supporting frames in the direction of the bridge correspondingly and are mutually parallel, the two ends of each carrying pole beam both extend out of the ranges of the pile foundations, a bracket is hung at each end of each carrying pole beam, the upper end of each bracket is movably connected with the corresponding carrying pole beam and can move up and down, the lower end of each bracket is provided with a platform capable of bearing objects, and the two formwork main beams are horizontally erected between the brackets, on the same side, of the two carrying pole beams correspondingly, so that a framework base plate can be erected. According to the adjustable straining beam construction formwork based on the pile foundations, through the adjustable brackets, the operation environment is improved, underwater operation is changed into overwater operation, the operation efficiency of mounting and dismounting the straining beam formwork under different water level conditions is improved, the window phase of construction is prolonged, and the operation time of the straining beam at different design water levels can be ensured.