Abstract: The aim of the present study was to evaluate the effect of drought on nature herbage in Evenk grassland of Inner Mongolia in 2015 and to assess the effect of climate condition and soil moisture on growth of herbage. During the critical period（from June 15 thto July 20th） for water requirement of herbage growth in Evenk region, the precipitation was reduced by 75.8%compared with that of the corresponding period of the previous years; the temperature was 1.7 ℃ higher than that of the corresponding period of the previous years; the lowest relative humidity of 0- 20 cm soil layers was 14.6% which belonged to the very dry soil moisture. In July 31 st, the aboveground biomass fresh weight was decreased by 32.3% compared with that of the corresponding period of the previous years, and the herbage coverage was reduced by 12%. By analysis on the related data collected in Evenk region from 2014 to 2015, the maximum aboveground biomass was found to be significantly positive related to the total precipitation during the critical period for water requirement of herbage growth（two sides 0.05 level）, indicating that as the total precipitation increased or decreased by 1 mm, the herbage production would increase or decrease by 19.7 kg/hm2.