Abstract: Assembly Box Concrete Hollow Floor is a new-style whole structure—with a cross section of a concrete box composed of small prefabricated components (concrete superposition box) and a cast-in-place concrete rib beam. The mechanical performance of the structure is analyzed in this paper based on the experiment with the test blocks of assembly box concrete hollow floor, and the failure mechanism affected by the load of floor is obtained. The findings prove that the prefabricated box and the cast-in-place concrete rib beam could interact, and in the calculation of floor framing design, a simplified flexural computing could be used, and each rib beam is taken as one computing unit. The top floor of the box could be used as the compressed flange, and the effective width of the compressed flange could be the sum of the two smaller figures, which are of the depth of 12 times of the box floor and the width of the cross section and the net span of a rib beam. The steel bars installed in the tensile area of the bottom floor of the box could fully exert its role, which could be taken into account in the flexural computing. The rack space and width in the bottom box floor of the tensile area are different from the cracks of the rib beam. The crack of the floor should be computed in accordance with reinforced concrete axial tension components, and that of the rib beam should be done according to the flexural member.