Fabricated steel structure and prefabricated building

The invention discloses a fabricated steel structure and a prefabricated building and relates to the technical field of prefabricated buildings. The fabricated steel structure comprises a floor slab assembly. The floor slab assembly comprises a pouring body, a plurality of beam bodies and a plurality of bottom tensioned bars. The beam bodies belong to cellular beams. The plurality of beam bodies define or are partitioned into pouring grids. The plurality of bottom tensioned bars are crossed to form a bottom reinforcement mesh. The bottom reinforcement mesh is arranged in the pouring grids andarranged close to the bottoms of the pouring grids. The ends of the bottom tensioned bars extend into holes of web plates of the corresponding beam bodies. Concrete poured into the pouring grids serves as the pouring body. The fabricated steel structure and the prefabricated building have the characteristics that the bottom surface of the floor slab is smooth, beams have no downward protrusions and flexible space arrangem