Silver-based highly-reflective coatings are widely used in the manufacture of optical instruments. However, it is still difficult to achieve both high reflectivity and long-term stability of the protected silver-based mirrors simultaneously. Here the thermal stability of silver-based high reflectance coatings is investigated both theoretically and experimentally. Silver-based mirrors are annealed at different temperatures, and then are characterized by X-ray diffraction and UV-VIS spectrophotometer. The microstructure of Ag-Cu alloy film is affected by the annealing temperature, which leads to the decreasing of reflectance of the alloy film with the increasing of annealing temperature obviously. (C) 2016 Elsevier B.V. All rights reserved.