The invention provides a cavity member for concrete hollow slabs. The cavity member provided by the invention comprises a reinforced concrete bottom slab (1) and at least two reinforced concrete side slabs (2), wherein the side slabs (2) are erected on the bottom slab (1) to form an elongated trough slab member. The cavity member is characterized in that an elongated trough of the elongated trough slab member is filled with at least two light filling blocks (3); the bottom slab (1) at the bottoms of the side slabs (2) is provided with at least one longitudinal full-length prestressed reinforcement (4); the tops of the side slabs (2) are provided with at least one longitudinal full-length prestressed reinforcement (4); the light filling blocks (3) are arranged at intervals, and inner-ribbed cavities (5) are arranged between the light filling blocks (3); the inner-ribbed cavities (5) are orthogonal or skew with the side slabs (2); the side slabs (2) in the space between the light weightfilled blocks (3) are provided with nicks (6); and the nicks (6) are provided with ties of tie piers (7) of the side slabs (2). The cavity member is suitable for the cast-in-situ reinforced concrete or prestressed reinforced concrete hollow slabs, hollow floors, roofs, foundation slabs, wall bodies and hollow bridges.