The invention discloses a prefabricated supporting bridge deck slab integral type steel-concrete hollow-out placenta formwork. The formwork is characterized in that before steel bar prefabricated slabsteel bars are bound, foam boards or plastic films are laid on the periphery and the bottom of base reserved grooves, so that influent cement paste when the bridge deck slab is poured is isolated, and cleaning is facilitated. The steel bars are bundled up on the base of the placenta formwork, and after the steel bars are bundled up, comb plates are inserted for fixing. The cement paste flown intoreserved notches through the gaps of the comb plates is flown into reserved holes of the base, so that the cement paste can be prevented from being connected with the supporting reserved notches intoa whole. After concrete is poured, surface finishing is carried out according to comb plate internal bridge deck slab surface finishing marks, then the upper surface of a 50 mm square steel tube or the upper surface of a frame tube is flush with the upper surface of the comb template and slides on the upper surface of the poured prefabricated plate, so that the surface of the concrete in the middle is uniform with the marks around, and the thickness and flatness of the prefabricated bridge deck slab are controlled. Through hollow-out structure in the placenta formwork base, the problem that the edge of the supporting reserved notches is damaged is solved, and the overall flatness of the bridge deck slab can be controlled through additionally arranged surface-finishing sliding rod.