A series of thin Ag films with different thicknesses grown under identical conditions are analyzed by means of spectrophotometer. From these measurements the values of refractive index and extinction coefficient are calculated. The films are deposited onto BK7 glass substrates by direct current (DC) magnetron sputtering. It is found that the optical properties of the Ag films can be affected by films thickness. Below critical thickness of 17 nm, which is the thickness at which Ag films form continuous films, the optical properties and constants vary significantly with thickness increasing and then tend to a stable value up to about 40 nm. At the same time, X-ray diffraction measurement is carried out to examine the microstructure evolution of Ag films as a function of films thickness. The relation between optical properties and microstructure is discussed. A series of thin Ag films with different thicknesses grown under the identical conditions are analyzed by means of spectrophotometer. From these measurements the values ​​of refractive index and extinction coefficient are calculated. The films are deposited onto BK7 glass substrates by direct current (DC) It is found that the optical properties of the Ag films can be affected by film thickness. Which critical thickness of 17 nm, which is the thickness at which Ag films form continuous films, the optical properties and constants vary significantly with thickness increasing and then At the same time, X-ray diffraction measurement is carried out to examine the microstructure evolution of Ag films as a function of the film thickness. The relation between optical properties and microstructure is discussed.