Abstract: Resonance characteristics of sub-wavelength gratings in the visible region are studied.The basic physical principle of resonant gratings is analyzed.Based on the rigorous vector diffractive theory,various optimization design plots about different grating parameters such as the grating period,filling factor,grating depth,grating materials et al,are provided.Detailed and accurate quantitative information on how various grating parameters affect the optical characteristics of the resonance device are given.The resonant wavelength is primarily determined by and directly proportional to the grating period.The full-width-half-maximum(FWHM) of resonance is mainly controlled by the grating modulation amplitude and the confinement of modes in the associated waveguide grating structure.The grating depth and filling factor have certain effects on the FWHM.These provide theoretical direction for the design of new optical anti-counterfeit devices.