A prefabricated superimposed recycled lump concrete slab includes a fresh concrete, demolished concrete lumps, and a reinforcement fabric at a lower part of the slab. The demolished concrete lumps can protrude from the fresh concrete, but a protruding height is no more than 25 mm, and the protruding height is controlled by assembling molds. The assembling molds comprise casting molds and a height-controlling cover plate, reinforcement-locating slots are reserved on side molds of the casting molds, and a vertical position of the height-controlling is determined by using screws, position-controlling nuts and gaskets of different thicknesses, which are located at four corners of the casting molds. A construction method of the prefabricated superimposed recycled lump concrete slab is also provided.