Optical characteristics and damage thresholds of mirrors used in RLG Dither were introduced. A new mirror was design. The new mirror have a high reflectance mirror with very low absorption and scatter losses. Simultaneity, to avoid the UV degradation which comes from the He-Ne plasma, the new mirror fabrication material was carefully selected. Furthermore，Optical scattering and performance gainst damaging of the new mirror were discussed and compared to the results of conventional coatings. Finally, the new mirror was made by ion beam sputtering method and its optical properties were measured.