Silage is a kind of livestock storage feed, and its fermentation principle is through the fermentation of lactic acid bacteria, which produces lactic acid, lowers the pH value, and inhibits spoilage bacteria. Silage can be stored for a long time, reducing the loss of nutrients during the process and enhancing the stability of feed quality. By controlling the fermentation process, the growth of miscellaneous bacteria can be inhibited, and mildew and rot can be prevented. This chapter focuses on the principles of fermentation and storage related to changes in microbial population structure and metabolites during silage fermentation.