The invention provides a leveled middle span side slab of a prefabricated sound insulation slab. Frame beams, slab edge joists and intra-slab joists are parallel to one another. The frame beams and the slab edge joists are arranged on the outermost sides of the upper end and the lower end correspondingly. The intra-slab joists are arranged between the frame beams and the slab edge joists. Preferably, the frame beams, the slab edge joists and the intra-slab joists are equally spaced. Frame beam reinforcing plates are arranged on the outer sides of the frame beams. A plurality of end cross supports are arranged between the frame beams and the intra-slab joists. Sound insulation material baffles are arranged at the left ends and the right ends of the frame beams, the intra-slab joists and the slab edge joists correspondingly. A floor top slab and a floor bottom slab are nailed on the two sides of the frame beams, the intra-slab joists and the slab edge joists correspondingly. A defined structural cavity is filled with sound insulation materials. The leveled middle span side slab of the prefabricated sound insulation slab has the beneficial effects that installation operation is remarkably simplified, the assembly speed is high, a large component assembly assembling mode can be adopted, the industrialization degree is higher, the economic effect is good, and environment pollution is avoided; and especially a sound insulation layer is internally embedded in the slab, field operation is greatly reduced, and the leveled middle span side slab is made to have good stress performance through a series of structures.