After corn silage and sweetpotato silage are ensiled, lactic acid bacteria grow and reproduce rapidly under appropriate conditions of water, carbohydrates, and anoxic conditions, and produce large amounts of ethanol and lactic acid, making the harder straws softer. Appropriate amounts of ethanol and lactic acid give the silage a good odor. This scent enhances the palatability and digestibility of the feed. However, when lactic acid and lactic acid produced by lactic acid bacteria are excessive, the acidity of silage is too high. Silage with too high acidity not only reduces palatability, but also has corrosiveness on the teeth of livestock, and also has greater irritation and corrosiveness to its stomach and intestines. So, how to control the acidity of silage? Practice has proved that adding appropriate amount of urea can control the silage acidity is too high, not only can reduce the acidity of silage, but also can increase the content of crude protein in silage and improve the nutrition of silage. The amount of addition and its method are: when silage, corn straw can be added 0.3% to 0.6% of urea; sweet potato can be added 1.2% of urea. When the moisture content of raw materials is too high, the urea can be evenly spread on the raw materials; when the moisture content of the raw materials is too low, the urea can be dissolved and stratified and evenly sprayed on the raw materials. In this way, the silage's acidity can be guaranteed.