Abstract: The multi-ribbed composite wall structure (MRCS) is a new structural system developed in recent years. As the main bearing member of MRCS, the multi-ribbed composite wall (MRCW) is composed of reinforced concrete ribbed-beams, ribbed-columns and light blocks. Material properties of MRCW are complex and elastic constants of MRCW are difficult to define. A micro-mechanics finite element method is proposed to analyze MRCW in the elastic stage in this paper. Selection of representative volume elements and boundary conditions, which are main problems in the solution process of effective elastic moduli of MRCW, are discussed. A micromechanics model suitable for MRCW is presented. Finally numerical and experimental results are compared. The results show that the micro-mechanics finite element model is more accurate and more applicable than the traditional model for calculating effective elastic moduli of MRSW.