The invention discloses a construction method of a bare rock low pile cap foundation, and relates to the technical field of bridge engineering. The construction method includes the steps that broken rock body construction is performed on an existing inclined rock surface at a design pier position, the slope of the inclined rock surface is controlled, and a construction surface is formed; a steel enclosure is designed according to the construction surface; a steel protection cylinder is inserted on the construction surface, and a lowering hanger is fixed to the upper part of a part of the steelprotection cylinder; a steel fence is lowered to the design position by the lowering hanger, in the steel protection cylinder which fixes the lowering hanger, the steel fence is locked with the adjacent steel protection cylinder, and the steel fence and the construction surface form a closed water-proof dock structure; and the bottoming concrete is poured into the water-proof dock body structure,water in the water-proof dock body structure is extracted, and then a pile foundation and a cap are constructed in the water-proof dock structure. According to the construction method, the closed water-proof dock body structure is formed by the steel fence and the construction surface, the construction quality is effectively guaranteed, the construction efficiency is improved, the operating environment is improved, meanwhile, the amount of temporary structural engineering quantity is reduced, and the construction cost is reduced.