The one-dimensional photonic crystals of Ag/SiO₂system are studied to investigate the photonic band gaps (PBG). The samples were prepared by the ultra-high vacuum electron beam evaporation. The clear band gaps were observed. Satisfactory agreement between experimental and calculated results was obtained without fitting. The thickness of SiO₂ film has influence on the photonic band gap, as well as it awfully affects the transmittance of Ag. More layers can get clearer PBG.