The possibility of antireflection (AR) coatings on a dielectric multilayer having sub-wavelength deep structural modification is investigated. We numerically surveyed the effect of reflectivity reduction attained by double-layer AR coatings for a wavy multilayer on a patterned substrate. It was clarified that double-layer AR coatings for wavy multilayer is possible with a similar performance level as conventional flat multilayer. Also, it was demonstrated that a pair of AR layers effectively works for a wide range of the horizontal pitch.