In order to trap more sunlight onto the crystalline silicon solar cell and improve the photo-electric conversion efficiency, it is very important to study the optical scattering properties of silver nanoparticles on silicon wafer. Based on localized surface plasmon effect and MIE scattering theory, using numerical calculation by Matlab, the scattering properties of solar spetra for different radius and density of silver nanoparticle are investigated in theory. The dependence of the optimal optical transmittance on the radius and density of Ag nanoparticle is obtained. Furthermore, it is found that the dipole peaks is redshifted and high mode peaks gradually emerges. Firstly this paper gives the variation of the best Ag nanoparticle density with the radius quantitively, the theoretical method calculating the transmittance of the nanoparticle antireflection film is also established. As a result, the simple functional expression of transmittance is deduced in this work, which provides a theoretical guidance for experimental research.