The present invention relates to a cavity mold-shell structural member which consists an upper plate (1), periphery side walls (2) and a lower plate (3), wherein the upper plate (1), the periphery side walls (2) and the lower plate (3) enclose a polyhedral hollow-cavity mould-shell structural member. At least one among the periphery side walls (2) and the lower plate (3) is made form light material (4) which is foam plastic, and the upper plate, periphery side walls and lower plate are all made from foam plastic. At least one among the periphery side walls (2) and the lower plate (3) is provided with at least a slice of a superposed layer. The cavity mold-shell structural member can be used for in-situ pouring reinforced concrete or pre-stressed reinforced concrete building cover, roof, base plate, wall, bridge and beamless building cover.