Cracking behavior of reinforced concrete composite floor slab, which has a significant effect on durability of concrete structures, is studied. Crack resistance of one-way composite floor slab is analyzed during transfer stage, handling stage, construction stage and serviceability stage, and calculation formulas are presented. Precast prestressed plank and topping cast-in-situ concrete layer can be designed as composite floor slab. It is assumed that prestressed unit is in elastic stage under service loads and hence every stress subentry can be calculated on the base of linear elastic theory and can be added linearly. For two-way composite floor slab, principal tensile stress in concrete is deduced on the base of theory of three-dimensional stress state in material mechanics. In addition, two-way effect on stress and practical distribution pattern of moment and shear force are considered. A number of structure experiment and experiences from engineering practice show that cracking behavior of reinforced concrete composite floor slab is a necessary consideration in design and analysis method shown in this paper is convenient and effective.