[Objective] The effects of enclosure on specie diversity of Xilamoren grassland in Inner Mongolia were studied in order to provide the scientific basis for the study of the grassland species diversity under the enclosure.[Medthods] This study analyzed the species diversity of enclosed grazing grassland based on the 11 years data of local annual precipitation in Inner Mongolia Autonomous Region.[Results] After enclosure, the interannual fluctuations of Artemisia frigida, Potentilla verticillaris, Cymbaria dahurica, Potentilla bifurca and Potentilla acaulis were larger. The diversity of the plants was reduced by the enclosure treatment. But Simpson ecological dominance index, Shannon-Wiener species diversity index and Pielous evenness index of the grassland plant in arid years were just the opposite in less precipitation years (2014 with annual precipitation less than 200 mm). Enclosure reduced the correlation coefficient between species richness and annual precipitation.[Conclusion] Enclosure treatment was not conducive to the plant diversity of Xilamuren grassland, but enclosure could alleviate the effects of climate change on species diversity under arid climate.