Stipa baicalensis is one of the main plant communities in grassland in Inner Mongolia and lawn ecosystem in Songnen plain in Northeastern China. The impacts of environmental condition change on C, N accumulation and distribution in Stipa baicalensis were studied. The simulation study shows that the CO_2 concentration in atmosphere enrichment increases root and leaf biomass, and soil drought decreases the root and leaf biomass. The C, N content was markedly increased along with the soil moisture increment, and the C, N content in CO_2 concentration enrichment is higher than that in ambient CO_2 concentration. It can be seen from the C, N distribution that the C, N content in leaf is higher than that in root. The increment of C, N accumulation because of CO_2 concentration in atmosphere enrichment decreases atmospheric greenhouse effect, and this effect would be increased along with the soil moisture sufficient. Under CO_2 concentration enrichment, the C/N ratio in Stipa baicalensis leaf decreases along with soil moisture increment. But, this tendency is not shown under ambient CO_2 concentration. The C/N ratio in Stipa baicalensis leaf is far smaller than that in root. It shows that the leaf nutrition value is higher.