Abstarct: The cobiax system is kind of appropriate slab that removing the concrete ineffective reduces dead load and thereby reduces the displacement and longer spans. It often consists of hollow spheres of plastic compression usually made of Polyethylene or Polypropylene concrete is placed into the cavity of a network such as the slab creates and formats such as flat slabs can be easily done. Thereby reducing the weight of the concrete intake of slabs with larger openings are pre-tensioned cables can be used without. In discussing the optimization of factors affecting the hardness and strength of cobiax roof can be slab thickness, the size of the balls, the balls away, long span steel profile and the concrete was studied. The size and spacing of the balls has a great effect on the stiffness and strength cobiax slab, with larger spheres reduced dead weight and the stiffness of the roof slab is reduced. It is desirable the dead load of concrete (concrete ineffective) until we have less effect on the shift and reduce the stress of higher strength and stiffness, this is optimal. In this study firstly, a model and a laboratory prototype to achieve similar results in vitro model to evaluate the accuracy of the finite element software and finally slab with different thickness and size of the spheres was studied and the results are shown on the chart, and this is achieved through optimum dimensions for the spheres.