A new method for calculating the elastic lateral stiffness of the multi-ribbed composite slab by ANSYS—the layered-shell element method is introduced in this paper. In the modeling process, there are two ways for establishing the model using element SOLID46: the first refers to regarding the slab as a whole to make arranged layers. While the second type suggests that making arranged layers in each part already separated according to the materials. Especially when there are reasonable hypothesis, the analysis results can guarantee certain precision. By comparison among the two models and the experimental results, no errors with each other have exceeded 5%. The whole model is used for the numerical simulation in view of its briefness. Several factors affecting elastic lateral stiffness are considered, mainly including elastic modulus of the concrete, elastic modulus of the brick, and number of the ribbed-column. From the calculating results, conclusion can be deduced that all of these factors affecting the slab’s stiffness significantly. Along with the factors’ rising, the elastic lateral stiffness of the wall grows up. Basically, the influence factor and the elastic lateral stiffness of the slab present to be linear relationship. It is also meaningful to see that the elastic modulus of the brick plays a very important part in the elastic lateral stiffness of the wall. When compared to the SOLID65 and LINK8 used for the slab’s modeling before, the layered-shell element method is simple in principle, and distinct in conception. Above all, because only one type of element in the finite element analysis is used, it will cost less time when used on building a model of integrated architectural construction.