Abstract: Outer-horizontal walls of multi-ribbed slab structure are composed of composite-double wall, based on the previous studies of the subject, and by researching on the test of a 1scaled multi-ribbed composite-double wall under monotone horizontal loading in contrast with single wall, the follovings are done: studying the main failure patterns; discussing the mechanical behaviors such as bearing capacity, stiffeners, distortion capacity, ductility and so on; analyzing the strain; finally, the formulas of rigidity and shear-bearing capacity are deduced. It can be concluded as follow: the distortion capacity and ductility of the double wall are better than those of the single wall, and the stiffeners and shear-bearing capacity of the double wall are more than those of the single wall also; strain analysis shows that the ending columns and ribbed beams play a more important role in the double wall with; the value of the shear-bearing capacity formula and stiffeners formula are approximate to the experimental result, and can be applied to the practical engineering.