Exogenous nitrogen addition can alter plant growth and community structure, thereby influencing soil carbon and nitrogen storage and ultimately impacting ecosystem services and functions. Previous studies have primarily focused on the effects of biological or abiotic factors on soil carbon and nitrogen storage in alpine meadows, but there is a lack of research investigating changes in soil organic carbon and total nitrogen storage as well as their controlling factors under nitrogen addition. Therefore, this study examined soil organic carbon and nitrogen storage across four levels of nitrogen addition. The results showed that nitrogen input significantly increased soil organic carbon and total nitrogen storage. Soil total nitrogen storage was positively influenced by soil total nitrogen, graminoid importance value, soil available nitrogen, and plant belowground biomass, while it was negatively affected by soil bulk density. Soil carbon storage was positively affected by soil organic carbon and soil nitrate nitrogen, and negatively affected by soil bulk density and forb importance value. This study emphasizes the positive effects of nitrogen addition on the accumulation of soil organic carbon and total nitrogen storage and highlights the combined effects of plant traits and soil physicochemical properties on soil total nitrogen storage.