以自上向下热蒸发大型镀膜机为实验平台，开展了逆向蒸发制备大口径银反射镜研究.通过设计特殊蒸发舟及优化相关工艺参数，实现了金属银膜稳定、高速向下蒸发.根据逆向热蒸发工艺特点，选取熔点低、升华型材料Cr和SiO及特殊设计的蒸发舟，以Cr或CrNx为粘结层，SiOx或SiOxNy为保护层，制备了三种具有四层结构的介质保护性银反射膜，并对所制备反射镜样品的反射率、断面形貌和环境稳定性进行了表征.实验结果表明：膜系结构为3 nmCr/120 nmAg/0.6 nmCrNx/150 nmSiOxNy的银反射膜具有较好的环境稳定性和光谱特性;通过了24小时湿热实验（50℃/相对湿度98%）和盐雾实验，在400～1 800 nm波段光谱范围内，银反射膜的平均反射率达到97.8%.

By using a high-vacuum resistive heating evaporation coating machine with the materials evaporated downwards, the research of downward thermal evaporation for large-aperture optics was implemented. The silver coating was prepared at a high deposition rate by resistive heating tungsten filaments without splashing. The adhesion layer and protective layer were also thermally evaporated downwards with specially designed evaporation boats with Cr or CrNx as the adhesion layer and SiOx or SiOxNy as the protective layer. To evaluate the performance of the protected-silver coating, three kinds of protected-silver coatings were prepared and researched in details. The reflectance, cross-section morphology and environmental stability of the prepared coating samples were characterized. The results show that the coating with 3nmCr/120nmAg/0.6nmCrNx/150nmSiOxNy structure has good performances on environmental stability and spectral characteristics. Especially,it has an average reflectance of 97.8% in the 400~1800 nm spectral range , and passed the tests of 24-hour humidity (50℃/98% RH) and salt folg.