The invention relates to the construction field of a highway bridge, in particular to a sinking-assistant construction method for sinking a sunk well, comprising the following steps of: (1) uniformly embedding hollow sinking-assistant pipes around the outer periphery of the well wall of the sunk well in the position 0.8-1.2m far away from the outer side of the well wall of the sunk well (1); (2) compressing high-pressure air into the upper end of each sinking-assistant pipe through an air compressor by pipelines to loosen soil bodies around the sunk well; (3) injecting high-pressure water to the sinking-assistant pipes from the upper end of each sinking-assistant pipe through a high-pressure water pump to destroy the soil bodies at the periphery of the sunk well, thereby reducing the sinking resistance of the sunk well; and (4) checking whether the sunk well is sunk in place, if not, sustaining 25-35 minutes, newly returning the step (2), and then finishing after the sunk well is sunk in place. By repeatedly adding the high-pressure air and the high-pressure water in the sinking-assistant pipes in the method, the soil bodies around the sunk well can be loosened so that the sunk well can overcome the resistance of the soil bodies through dead weight to sink in place along the preset sinking way.