[Objectives]  Precipitation and grazing are important factors that drive grasshopper outbreaks in grassland ecosystems but exactly how these factors affect grasshopper population dynamics remains controversial. To clarify this, we studied the combined effects of sheep grazing and seasonally increasing precipitation on variation of both total C and N content, and available C and N content, of grasshopper food plants. [Methods]  Using both field studies and laboratory experiments, we investigated the development and survival responses of D. barbipes under different grazing and precipitation treatments. [Results]  Grazing can significantly decrease the C content in soluble sugar, and the available C content of the leaves of Leymus chinensis, but did not significantly affect the C content of starch or total C. Grazing also significantly increased the N content of amino acids, available N, total N, and the available C : N ratio. However, it had no significant effect on the N content of protein. The effect of seasonally increasing precipitation on C and N varied between grazed and ungrazed treatments. Increasing precipitation tended to reduce the C content of soluble sugar and the N content of amino acids, but the differences among precipitation treatments were not significant. Moreover, the results of a laboratory experiment suggest that grazing significantly decreased mortality, shortened developmental duration, increased growth rate, and increased adult body weight of fifth instar nymphs to adults, whereas the results of a cage experiment conducted in the field indicate that grazing increased survival and the development rate. Nevertheless, increasing precipitation did not significantly affect any biological parameters of D. barbipes. [Conclusion]  Suitable grazing was propitious to the growth, development, survival of D. barbipes, and could promote grasshopper outbreaks by decreasing the C content of soluble sugar and increasing the N content of amino acids in food plant leaves.