The invention belongs to the technical field of construction of cast-in-place reinforced concrete beams through a support method in bridge engineering construction, particularly relates to a method and device for pre-pressing a high-position support single column in water, and solves the problems in existing beam column type support preloading of being more in investment, long in construction period, large in energy consumption and the like. The method includes the steps: installing an upper traction system, a middle connection system and a lower loading system, arranging ballasting according to levels, conducting measurement according to levels, and unloading and removing a pre-pressing device according to levels. The device comprises the upper traction system, the middle connection system and the lower loading system. The upper traction system comprises two winches and two distribution beams. The middle connecting system comprises a traction steel wire rope, the traction steel wire rope is connected with a pulley block, and the pulley block is connected with the lower loading system. By means of the method and device, a purpose of pre-pressing a support structure is achieved, hoisting and unloading of piled things in a pre-pressing process and manufacture and storage of a large amount of piled things are avoided, and the problem that a pre-pressing material is hard to recycle, and device is high in power and the like is solved.