Abstract: In order to optimize the structure parameters of the device, the period, height and duty ratio of grating structure were taken as the optimized particles. By using particle swarm optimization algorithm and rigorous coupled wave analysis algorithm, fitness values of the particles in particle swarm were compared. After theoretical analysis and simulative optimization of the structure of metal-medium grating filter, the optimal parameters were found in a certain range. The results show that, according to MATLAB simulation results, structure parameters are optimized:period is 0.300μm, the thickness of metal grating is 0.035μm, the thickness of dielectric grating is 0.400μm and grating duty ratio is 0.77. When TM light is vertically incident, the transmission rate of structure to red light in 0.65μm wavelength is 80.27% and the transmission rate of the side bands is less than 15%. This structure achieves high transmission to specific wavelength light and then achieves light filtering. This structure provides the reference for the design, fabrication and practical application of sub-wavelength gratings.