Abstract: The regulation mechanism of plant population structure and function by herbivores is an important part of grazing ecology. A long-term grazing study in Xilingol was used to reveal the mechanisms of the regulation of plant responses to grazing through population age dynamics and leaf traits of Stipa breviflora in desert grassland. The result showed that few S. breviflora plants with base diameter of less than 4 mm survived. There was little difference between moderate grazing and no grazing. The frequency and proportion of age class Ⅲ plants was reduced 0.79 and 0.73 respectively by heavy grazing. S. breviflora population were relatively stable. Two way ANOVA showed that leaf height, leaf length, leaf dry weight, leaf erectness and leaf length-width ratio were sensitive to grazing in different age classes. By contrast, leaf width, leaf rolling index and leaf dry matter content were not affected by age class. Correlation analysis suggested that leaf width and leaf dry matter content changed synergistically with the age sensitive traits. Leaf rolling index was significantly negatively correlated with leaf dry weight, and was positively related with leaf erectness (e.g. age class Ⅲ and class Ⅰ). The study suggested that S. breviflora completed its life history and adapted to grazing by controlling population age and leaf traits in a metastable state.