The invention relates to a hollow floor of a rectangular steel tube concrete multi-ribbed beam structure and a construction method, and belongs to civil engineering structures and construction methods. The hollow floor is characterized by comprising rectangular steel tubes, opposite-pull rebar, ribbed beam longitudinal bars, a prefabricated bottom plate, bumps, stiffeners, multi-ribbed beams, a cast-in-situ top plate, top plate rebar, side templates and a top template; the top pipe wall, the front pipe wall and the rear pipe wall of each rectangular steel tube are provided with slots, the opposite-pull rebar and the ribbed beam longitudinal bars, the prefabricated bottom plate is arranged among the four rectangular steel pipes, the side templates are arranged on the four sides of the prefabricated bottom plate, the top template is arranged on the side templates, a cavity is formed among the prefabricated bottom plate, the side templates and the top template, and the ribbed beam longitudinal bars, the top plate rebar and a cast concrete layer are bounded to form the hollow floor. The construction method comprises the steps of construction preparation, bottom template erecting and rectangular steel tube hoisting, prefabricated bottom plate, side template and top template installation, ribbed beam longitudinal bar and top plate rebar binding and concrete pouring. The hollow flooris reasonable in structure, high in bearing capacity, simple in technology and good in quality.