The invention provides a prefabricated concrete composite floor slab with adjustable height. The prefabricated concrete composite floor slab comprises angle steels, soft material, a steel bar truss, L-shaped screw rods, concrete and nuts. The concrete and the steel bar truss are jointly poured in a factory to form a component A1 with holes in both sides, and slotting hole angle steels are placed at the bottom of the component A1 in a hole-aligned mode. Vertical rods of the L-shaped screw rods on the site penetrate through the component A1 and holes of the angle steels and are tightened by nuts, and cross bars are hung on the upper surfaces of beams during lifting. After lifting, the height of the prefabricated floor slab is adjusted by adjusting the nuts on the L-shaped screw rods, the relative position of floor slabs and the beams is adjusted, it is ensued that the surfaces of the floor slabs are flush, and the assembly problem caused by the uneven surface of a concrete component is solved. The prefabricated slab and the angle steels serve as a bottom formwork, gaps are filled with the soft material to prevent slurry leakage, and pouring of a post-poured layer is facilitated. Partof the beam height is invisible from the floor slab, and the clear height of a structural layer is increased. The steel bar truss in the prefabricated floor slab enhances the adhesion of new and oldpouring layers, and the integrity of the prefabricated concrete composite floor slab is improved.