As a new structural system, MRSS (multi-ribbed slab structure) has some applications in multistory building. But theoretical investigation and application study on multi-ribbed composite wall in high-rise building should be developed with various factors composing shear resistant capacity of wall under complicated loads. By means of model test and numerical simulation with FEM (finite element method), shear resistant expression of slab in tall building is set up and reliability index of a representative wall under small earthquake is figured out. Sensitivity of each factor affecting shear strength is evaluated. These works disclose the wall’s load bearing mechanism and make the structure application more feasible and assure the new system safety in practice.