Abstract: Composite floor slab，as one of major steel frame structural elements，could greatly influence the antiprogressive collapse performance of structures． But the influence of slabs was not taken into consideration in the existing researches． In this paper，based on the two-way tension model of composite floor slab ， the mechanical behavior of composite floor slabs in the process of progressive collapse was analyzed，and established a simple calculation method of ultimate bearing capacity at failure point considering the tie force of slabs． Progressive collapse analysis of frames based on the simplification model is simulated by the finite element method，in order to validate the simple calculation method，and investigate the slab’s influences on plastic hinges，ultimate bearing capacity，amplitudes and periods of dynamic response at failure point，the result shows that slabs can effectively enhance the performance of structure to prevent progressive collapse．