In this research, the effects of geometrical parameters (length, diameter and surface density) of Nano Rod Array (NRA) of  ZnO coated with Al doped ZnO on variation of refractivity of solar cell antireflection coating are investigated. The reflectance behavior is simulated by FDTD Commercial Software Lumerical 2015. Maxwell equations are solved with Lumerical software based on finite difference time domain method and electric and magnetic fields are evaluated in space. By using these solutions and hemispherical reflectance method, reflectance is calculated. Simulation results show that variation of Geometrical parameters of NRA (diameter, length and surface density) has no significant effect on reflectance. However, using NRA influence on uniformity of reflectance amount for different incident angles.