Silver nanoparticles are formed by ion implantation into amorphous silica matrix at 200 keV at room temperature with doses of 1×1016, 5×1016 and 1×1017 cm-2. The sizes，distributions and shapes of the silver nanoparticles in the samples were obtained by transmission electron microscopy, which is greatly influenced by the dose. The effect of size，distribution and shape of the silver nanoparticles to the optical resonant absorption peak is been discussed. Optical absorption spectra of samples implanted with 5×1016 and 1×1017Ag+ cm-2 showed absorption peaks shifted to red, the intensity of absorption peak increased and shoulder peaks appeared, compared with the absorption spectra of the sample implanted with 1×1016Ag cm-2. The red-shift of absorption peaks and the appearance of shoulder peaks are due to the increasing volume factor and the multipolar plasmon induced by the interaction of nanoparticles, respectively. Raman scattering spectroscopy indicates that there are many defects in the high-dose implanted samples. Nanocavities in the large Ag nanoparticles are discovered in the sample with the dose of 1×1017 cm-2 possibly due to the aggregation of implant-induced silicon and oxygen atoms in Ag nanoparticles.