Compared with traditional optical multilayer coating method, the two-dimensional subwavelength periodic structure can achieve better anti-reflective effect with the easy adjustment of the whole structure’s refractive index, by varying the structural parameters, such as the size and the period. Based on the finite element method of full-wave electromagnetic field analysis, we investigate the periodic subwavelength structure of closely-packed nano-particles, and study on how the geometry of the structure affects the reflectivity. We also prepare different sizes of silica nano-particles by using the sol-gel method, and fabricate anti-reflective samples with these particles. Reflection measurement of the samples showed good anti-reflective performance at optical range. Finally we propose a practical method for designing periodic antireflective subwavelength structure of nano-particles on the basis of both theoretical calculation and experimental verification.