Abstract: The effect of thickness on the residual stress and microstructure of Ag-MgF₂ cermet films prepared by vapor deposition is introduced. The X-ray diffraction（XRD） technique was employed to study the microstructure of the films. The results show that the average stress over a φ20.4 mm round area is the least and the residual stress of the films appears to be press stress at 130 nm thickness.The rule of chang rate of crystal lattice constants of Ag with thickness accord with that of residual stress of film. The effect of Ag grain structure on the residual stress and microsturcture of Ag-MgF₂ films is greater than that of MgF₂.