Abstract: In order to calculate the shear bearing capacity of cold-formed steel (CFS) composite walls with lightweight gypsum infillings, the full scale specimens including two unfilled walls and nine infilled walls were tested under reversed cyclic loading. The failure modes of the walls under horizontal loads were studied. The test results show that the failure modes of unfilled CFS walls are characterized by the screw connections between sheathings and CFS frames, thus causing the loss of stressed skin provided by sheathings. There are two possible failure modes of CFS walls with fillings. One is the compressive failure at the corner of gypsum fillings, and the other is the flexural failure of CFS studs. According to above-mentioned failure modes and limit equilibrium theory, a shear bearing capacity calculation model based on superposition method is proposed considering the contributions of sheathings and infill materials. Then the calculation equations of shear bearing capacity are also derived. The model can reflect the impact of screw connections strength, infill material strength and CFS frames strength on shear bearing capacity of the walls. The ratios of the theoretical calculation values to the test values are between 0.947 and 1.112, which demonstrates that the theoretical calculation values have a good agreement with tests values.