In order to investigate the in-plane stiffness and bearing capacity of cold-formed thin-walled steel composite floor, a floor model was established through ABAQUS software and verified by the in-plane cyclic loading test results. Further, the effect of different parameters on the in-plane stiffness and bearing capacity of the floor model was studied. The results showed that the influence of the joist size，the opening area and spacing of joist web, flat strap and blocking layout on the in-plane stiffness and bearing capacity of composite floors was insignificant. The in-plane stiffness and bearing capacity of composite floors can be improved by decreasing the screw spacing and the length-to-width ratio of floor. The change of slab thickness in the range of 20~40 mm had a certain effect on the in-plane stiffness and bearing capacity of composite floors. Based on the failure modes and mechanical behavior of composite floors, the ultimate bearing capacity of floor can be estimated by the load-carrying capacity of the single self-tapping screw and the number of self-tapping screws connected on both sides of floor. The calculation method for in-plane stiffness of composite floors was established based on the degenerate quadri-polyline model, which provided a theoretical basis for engineering design and application of thin-walled steel floors.