Subwavelength gratings with different grating parameter have different diffractive properties, and realization of nonpolarizing narrow-band filtering by reasonably designing the parameter of subwavelength grating is a novel method and approach. Based on resonant anomaly, physical mechanism of narrow-band filtering and its condition was analyzed, and probability for realization of nonpolarizing narrow-band filtering in two-dimensional subwavelength gratings was discussed. Using rigorous modal theory, its simulation results were consistent with those of guided-wave theory, in which location of resonant anomaly appear periodically and diffraction efficiency is very sensitive to not only incidence angle but also wavelength. At last, fabrication errors effecting diffractive properties were analysed, which, to some degree, are useful to concrete fabrication.