Periodic sub-wavelength nanocones were simulated for antireflection with three different heights: 300, 500 and 700 nm on Si substrate. On the top of nanocones, we add a layer of Ni and S i with the thicknesses of 10 nm, 20 nm and 30 nm. The reflective characteristics of nanostructures with or without nanomasks were studied by rigorous coupled-wave analysis (RCWA).