Herein, a bilayer sub-wavelength metallic grating structure is optimized in the visible-light band using genetic algorithm and finite-difference time-domain method to improve the grating performance. Through simulation analysis, the structure can achieve polarization filtering function of blue band with a maximum transmittance of 77%, maximum extinction ratio of 20 dB, and full width at half maximum of 35 nm. By analyzing the influences of grating parameters on grating performance, it is proven that the structure has a large process tolerance. In comparison with the conventional structure, the optimized grating has good transmission performance and filtering performance, and it has good application prospects in fields such as polarization navigation, polarization detection, display, and imaging sensing.