Abstract: Frame structures are mainly designed to prevent the progressive collapse through two resistance mechanisms under the condition of sudden destruction of vertical bearing components, including the beam mechanism under a small deformation condition and the catenary mechanism under a large deformation condition. The large planar stiffness of the composite slab can significantly improve the resistance of the progressive collapse of the structures. This paper simplifies a concrete floor-steel frame structure into a steel-concrete composite beam structure. The structure resistance curve obtained by previous researches is simplified. The mechanical characteristics in various stages during the progressive collapse are analyzed to obtain formulas of the resistance curve at every stages by using the energy method. Subsequently, the reliability of the proposed formulas is validated against a case study of an example by using the large-scale finite element analysis software ANSYS, and a good agreement is observed. It is shown that the slabs can greatly strengthen the progressive collapse resistance of the structures.