In this study, we analyze the changes of indicators of ecosystem services and functions, in order to understand the main cause of grassland degradation due to climatic variation or land use changes in the middle-south Inner Mongolia. The soil nutrient and the water supply of supporting service got recovery during 1988–2008. The loss of net primary production declined, and the quality of the retained unconverted grassland (RUG) even increasingly degraded from 2000 to 2008. Analytical results show that environmental degradation on the land-use-changed-area is lower than that on the RUG from 2000 to 2008. It illustrates that climatic variation has more negative impacts on grassland ecosystem service, and which is significantly higher than the so-called “overgrazing” induced grassland degradation. Moreover, it cannot be excluded that those species died out on the RUG due to natural selection or competitive evolution in an evolutionary process under the deteriorative weather condition rather than overgrazing. The positive impacts of human activities such as conservation programs and wildlife protection laws also benefit to regional grassland ecosystem obviously in the study area, so that can delay the environmental degradation even if each planet has its life cycle. It indicates that an integrated regional planning involving the considerations of climatic conditions, geographical characteristics, socioeconomic factors, and ecological functions and biodiversity can benefit to regional grassland conservation based on monitoring and management via scientific methods.