Abstract: Based on the low-frequency cyclic lateral loading experimental study of multi-ribbed composite wall, the paper describes the main failure processes and mechanical properties of the walls. The twin shear unified strength theory that can describe the behavior of various materials subject to complex stress states is applied in this paper and the influence of the intermediate principal stress 2 is considered. The practical computing formulas for the wall’s primary cracking load based on the theory above and the maximum tensile stress theory are comparably analyzed. The comparison results show that the former is more comparable with the experimental results.