Abstract: The relative soil moisture data observed by automatic soil moisture observation instrument of GStarDZN2 type were compared with the meteorological observation data and the drought conditions were objective analysis from 2012 to 2015 on Ewenki grassland. The results showed soil moisture from 0 to 30 cm in late June to mid July had a greater impact on the growth of natural grassland and the minimum relative soil moisture had a significant correlation with herbage yield. The average minimum relative soil moisture increase（decrease） by 1 percent,the herbage yield increase（decrease）by 10.4 g/m2.Automatic soil moisture observation instrument of GStarDZN2 type could express the drought conditions more accurately.