The invention relates to a horizontally slidable device and an application method in jack lifting and unloading construction, belongs to the technical field of building construction, and is used for solving the problem that in construction, a jack overturns due to horizontal displacement of a lifted object. The horizontally slidable device comprises a top plate, a bottom plate, balls between the top plate and the bottom plate, a steel sleeve arranged on the lower surface of the bottom plate and a limiting device positioned at the end part of the bottom plate, wherein a gap is formed between the top plate and the bottom plate; the top plate can slide horizontally relative to the bottom plate through the balls. The application method comprises the following steps: firstly, adjusting limiting rods of the bottom plate to position the top plate in a central position and lock the horizontal freedom degree of the top plate; secondly, sleeving the top end of the jack with the steel sleeve to connect the horizontally slidable device and the jack; thirdly, putting the jack at a preset position, and adjusting the elongation of the jack to tightly press the upper surface of the top plate against the lifted object; and finally, at the beginning of the construction, unlocking the limiting rods to ensure that the top plate can slide horizontally during the construction process.