To determine effects of grazing and enclosure on the ecological stoichiometry characteristics, we evaluated the carbon(C),nitrogen(N),and phosphorus(P) contents in soil and leaves of four plants, which were Festuca ovina, Leymus tiansecalinus, Potentilla bifurca and Potentilla anserine, inside and outside the fence of the Bayinbuluk Grassland Ecological Research Station, Chinese Academy of Sciences. The results showed that soil nutrient content of enclosed grassland was significantly higher than that of grazing site, except total nitrogen (TN) content (P<0.05). The enclosure significantly increased the content of C and N in the leaves of Festuca ovina (P<0.05), but it did not significantly affect the content of P. The enclosure significantly increased the C content (P<0.05), but it significantly reduced the N and P content in the leaves of Potentilla anserine. Effects of the enclosure on the nutrient content of Leymus tiansecalinus and Potentilla bifurca were not significant. The enclosure significantly increased C:N and C:P of Potentilla anserine (P<0.05), while it significantly reduced C:N, C:P and increased N:P of Festuca ovina(P<0.05). The enclosure significantly reduced C:N of Potentilla bifurca(P<0.05), but it had no significant effect on the stoichiometric characteristics of Leymus tiansecalinus. The different species had different responses to the enclosure, meaning that long-term enclosure may change the structure of the Tianshan alpine grassland ecosystem. The enclosure reduced the carbon sequestration capacity of the dominant plant species (Festuca ovina) and increased the carbon sequestration capacity of the forb (Potentilla anserine) in the degradation stage. In long-term enclosure, Potentilla anserine may provide more carbon for the soil, and it also could promote nitrogen and carbon content of the dominant grass species.