To improve the reflectivity of vertical alignment Liquid Crystal on Silicon (VA-LCoS), we built a three-dimensional (3D) optical modeling for the normally black VA-LCoS mode, and investigated the effects of the gap of liquid crystal cell, the pretilt angle of liquid crystal and wavelength of incident light on reflection for linearly polarized light and circle polarized light as incident light, respectively. As a result, the black zone in the on-state pixel was eliminated by using circle polarized light as incident light. Moreover, the VA-LCoS has the highest reflection as the cell gap is 1.6 μm. The results have an important guiding significance for the design and preparation of VA-LCoS.