By using of effective medium theory, the reflective efficiency of two dimensional surface relief structure is computed and analysised in various conditions through computation of rigorous coupled wave method. Several curves are presented in various conditions. Effective medium index of that structure is computed when plane wave normalized on the structure. It is indicated that variation of orientation and polarization angle make less effect on reflectivity for both symmetric or asymmetric structure. The result giving characteristic of anti polarization and anti reflective is obtained. The bandwidth limitation is analysised and its magnitude is given. While, the effect of manufacture error of relief height on reflectivity is analysised. It has a certain instruction significance to the practical work.