The invention discloses a filling die for manufacturing a prestressed hollow beam, which comprises four rectangular wood boards. The four rectangular wood boards are surrounded into an inner cuboid space. A board frame consisting of a plurality of wood boards is arranged in the inner cuboid space. The board frame is surrounded into a small-scale inner space. The middle part of the small-scale inner space is of a ridge shape. For the prestressed hollow beam manufactured by the filling die for manufacturing the prestressed hollow beam, which is disclosed by the invention, convex ribs can be formed on a bottom plate of the beam, so that the strength of the bottom plate of the beam is improved and longitudinal cracks are avoided being formed on the bottom plate of the beam.