Stipa baicalensis grassland is a type of meadow steppe that plays an important role in livestock husbandry in China. In recent years, unsustainable grazing, mowing, and other overuse patterns have heavily affected China's grassland ecosystems, resulting in decreased productivity and losses in biological diversity and ecosystem stability. The restoration and sustainable use of grassland ecosystems has become a concern in grassland ecology. Low levels of soil nitrogen (N), phosphorus (P), and potassium (K) often become important factors that limit grassland productivity, while arational application of N, P, K and medium trace element fertilizers can obviously promote the productivityand quality of grasslands. Nutrient addition can affect the structure and diversity of grassland plant communities, and studies on the response of grasslands to adding nutrients will have important theoretical and practical significance to the recovery, reconstruction, and scientific management of degraded grassland ecosystems. We studied the effects of added N,P, and K in a S. baicalensis grasslandto provide a basis for the rational use and protection of grassland resources and the restoration and reconstruction of degraded grassland ecosystems, as well as to lay a foundation for a more general analysis of the relationship between biodiversity and productivity.A randomized block design experiment was conducted with six blocks of eight treatments each: C (control, no nutrient addition), K (K addition only, 100 kg/hm²), P (P addition only, 100 kg/hm²), N (N addition only, 100 kg/hm²), PK (mixed P and K addition, 100 kg/hm²of each element), NK (mixed N and K addition, 100 kg/hm² of each element), NP (mixed N and P addition, 100 kg/hm² of each element), and NPK (mixed N, P, and K addition, 100 kg/hm² of each element).Forty-eight (8 m × 8 m)plots were established with 2 m and 5 m isolation belts between the subplots and main treatment areas, respectively. In 2010,nutrients were applied twice a year with 50% of the treatment amount applied on June 15 and 50% again on July 15 during the grass-growing season.Fieldwork was completed in mid-August during the grass-growing season in 2012. To eliminate edge effects,conditions were measured only in the 6 m × 6 m area in the center of each 8 m × 8 m plot.A 1 m² (1 m × 1 m)quadrat in each 6 m × 6 m plot was used to record various biological and ecological characteristics including plant composition, plant height,percent ground cover, and vegetation density.We evaluated these characteristics to estimate primary productivity and plant diversity. One-way ANOVA was used to calculate the species richness, the Shannon-Wiener and Pielou indices, and to analyze aboveground biomass. The relationships between the diversity indices and aboveground biomass were determined through linear regression. The results showed that all treatments increased primary productivity and reduced plant diversity. N addition, with or without P or K addition,always significantly decreased the Shannon-Wiener and Pielou indices (except for the NP treatment which had no significant effect), but only the NP treatment resulted in a significant decrease in species richness. With the exception of the K treatment,all treatments resulted in significantly increased primary productivity. Among the three nutrients, N was the most effective treatment in increasing plant productivity and diversity; the NPK treatment had the greatest effect, increasing aboveground biomass 1.31 times compared to that of the control. Nutrient addition altered the community structure in that N addition significantly increased the proportion of grasses and reduced that of legumes, but the effects of nutrient addition on the proportion ofcyperaceae and forbs were negligible. With fertilization, plant diversity (correlation coefficient, -0.522), species richness (-0.391), and species evenness (-0.534) were all negatively linearly correlated with primary productivity. In conclusion, the NPK combination treatment resulted in maximum grassland productivity while effectively maintaining plant diversity, resulting in improved environmental conditions and achievingsustainable development.