Abstract:Severe effects of human activities and the rapid growth of population on the environment result in the global change or the regional change, finally affecting the biological diversity at different scales. The grassland is a fragile ecosystem. Under the effects of natural factors and human activities, the grassland is very sensitive to the global or regional climatic changes. The present paper deals with the effects of regional climatic changes in 40 years on plant species diversity in Inner Mongolia. The results are as follows:1, During 40 years (from 1950 to 1990), the moisture was fluctuated due to the grassland regional climate change, and the amplitude and frequency of the fluctuation to the east were all great, especially the fluctuation of 0.3 moisture isohyet.2, In the core-zone of 0.3 moisture isohyet, the relative change rate and fluctuation variance for both the number of individuals and biomass among different sampling plots varied west-east to the adjacent area significantly, There was an increasing trend in species diversity index.3, The moisture isohyet was exactly located at ecotones. In general, the quantitative changes of the vegetation in ecotones were more sensitive than that in the core-zone. The abnormal results in this paper (The core-zone of 0.3 line was more sensitive than the ecotones of 0.13～0.3 and 0.3～0.6) were exactly caused by the effects of regional climatic change.