Abstract: In order to promote the rational utilizati on of grassland,nitrogen addition was continuously carried out in 2021 and 2022, and the indexes of crude protein,crude fiber,crude fat and crude ash of sample plots and main plants were determined.The principal component analysis method was used for quantitative comprehensive evaluation to explore the effect of nitrogen addition on the feeding quality of main plants in mountain grassland.The results showed that the order of nitrogen levels of grassland plants was:Digitaria ischaemum＞Agropyron cristatum ＞Carex duriuscula ＞ Lespedeza daurica ＞ Cleistogenes squarrosa ＞ Medicago ruthenica.Short-term nitrogen addition could significantly increased the contents of crude protein,crude fat and neutral detergent fiber in mountain grassland plants,but had no significant effect on acid detergent fiber,crude ash and dry matter yield.With the increase of nitrogen ratio,the contents of crude protein, crude fat,neutral detergent fiber and dry matter yield in the community increased first and then decreased,while the contents of acid detergent fiber and ash decreased.The application of nitrogen fertilizer can significantly improve the nutritional value of gramineous plants,but has no significant effect on leguminous forage.The nitrogen application rate that could significantly improve the nutritional value was O₄I₀(organic nitrogen 4 g·m^-2).