Since 1981, the long-term vegetation data at Leymus Chinensis grassland in Inner Mongolia has been collected. This paper analyzes the triple relations among the vegetation, temperature and time based on the smoothed data that were treated with the method of moving average. The results show that the average minimum and maximum temperatures in winter (Oct. to Mar.) in this region increased faster than that in summer (Apr. to Sep.), and that the yearly average minimum and maximum temperatures increased from 1981 to 1994 mainly because of the increasing of minimum and maximum temperatures in winter, which were in line with the trend of global warming. In the meantime, the first 6 dominant species of this grassland responded to the temperature changes differently： the Importance Value (IV) and Aboveground Net Primary Productivity (ANPP) of the first, third and fifth dominant species, Leymus chinensis, Cares duriuscula, and Artemisia commutate, respectively, decreased because of global warming, and the IV and ANPP of the second, fourth and sixth species, Stipa grandis, Achnatberum sibiricum, and Agropyron michnoi, respectively, increased owing to species compensation for utilizing resources. So the Stipa grandis, the second constructive species, may replace Leymus Chinensis, the first constructive species, and gradually become the first one if these trends continue, and the structure and function of the community would change. Therefore the interaction of competition and compensation among dominant species should also be paid attention to when we study the response of species at the Leymus Chinensis grassland to the changes of temperatures, which is conducive to understanding the dynamic mechanism of individual species and entire community.