Introducing silica dielectric film deposited by magnetron sputtering on silicon substrates, the dependence of the surface coverage ratio, morphology, formation mechanism and optical properties for silver nanoparticles on silica dielectric film was exploited. The results indicate that the surface coverage ratios of silver nanoparticles increase but the mean diameters for silver nanoparticles decrease obviously after introducing silica dielectric film. The reason of morphological evolution for silver nanoparticles was explained by an improved model for silver film rupture based on the formation mechanism of silver nanoparticles. A red shift of up to 86 nm of the dipole extinction peak of silver nanoparticles is realized by adjusting the thickness of the silica film but the peak intensity decrease greatly, as analyzed by an ultraviolet-visible spectrophotometer. Numerical simulations of the optimized structures demonstrate that the number of scattered photons by the silver nanoparticles is decreased by as much as 2×1018 after inserting a silica layer. Therefore, it is undesirable to deposit silica layer on silicon substrate before silver nanoparticle formation for the light trapping performance of silver nanoparticles.