Composite shear walls made of a thin steel plate with reinforced a concrete cover, which is attached to one or both sides of the steel plate, are the third generation of lateral load resisting shear walls. In addition to increasing resistance, ductility and energy absorption, these walls are very economical and are used in constructing tall buildings, resistance of buildings and tanks. In the present research the effect of various thicknesses of steel plate on the behavior of composite shear walls in different shear connectors has been studied. For this purpose, several different models, including moment frames, steel shear walls and composite shear walls, have been analyzed through numerical and experimental models. In composite shear walls, the number of layers of reinforced concrete cover, the distance between the shear connectors and the thickness ratio of steel plate to the thickness of concrete cover are considered as variables. Increasing the thickness ratio of the steel plate to the concrete layer up to optimum leads to reduction in the out-of plane deflection rate of the steel plate and has no effect on the performance of the composite shear wall. In addition, using two layers of concrete cover on both sides of the steel plate decreases the secondary moment.