The invention is a cast-in-site concrete hollow slab, comprising reinforced concrete, and box-like forms, where the box-like forms are wrapped in the reinforced concrete, top casing, peripheral side casing and bottom casing compose a box-like form, and cast-in-site reinforced concrete ribs are formed between the box-like forms, and it is characterized in that: at least one of the top casing, peripheral side casing and bottom casing is a whole stacked and cemented by wet body casing and prefabricated body support component, and the prefabricated body support component supports the wet body casing for shaping. Thus, it has features of simple structure, high intensity, large rigidity, excellent deformation and vibration resistances, high construction speed, etc, and it is applied to cast-in-site reinforced concrete or prestressed reinforced concrete hollow building covers, roofs, wall bodies, foundation soleplates and bridges, especially hollow, beam-free building covers.