Based on the strict and long-term grazing test and quadrate investigation, we revealed the dynamic succession of plant community and species diversity as well as mechanism of species losses under the grazing condition. The main results are (1) The community appearance characteristics and composition become dividing obviously under stable different grazing pressure. (2) The continued intensive grazing causes the species losses and decrease in a diversity, this provides partly basis for understanding the modern species disappearance and extinction. The species extinction was due to destruction of habitat by human being. Destruction of habitat leads to species disappearance in local istrict. Accumulation of the species losses in local district may lead to the species true extinction. (3) The grazing influence the species composition and (3 diversity in both the temporal and spatial dimensions.