Abstract: Many open-pit mines in the grassland area of eastern Inner Mongolia are threatened by river surface water and quaternary loose layer water.It is found that the groundwater distribution characteristics have become an important thorny task for mines in this region.This paper takes an open-pit mine in eastern Inner Mongolia as the research object,using nuclear magnetic resonance exploration method,six exploration lines are arranged in the north of the mining advance direction,and two sections are divided from west to east.The results show that there are six horizontal maximum moisture content in the first section,and the area with the maximum water content of 20% is about 500-700 m in the section of exploration line 1.The second section has the maximum water content in four horizontal planes,the moisture content range is mainly distributed in the section 1 900-2 100 m of prospecting line 3,line 4,line 5 and line 6,and the maximum water content is about 14%.Nuclear magnetic resonance technology determines the groundwater aquifer distribution,thickness,moisture content and water-rich area of groundwater aquifer,and the inversion results are basically consistent with the lithology of rock strata,the pumping effect of pumping wells verifies its accuracy,which provides detailed geophysical data for waterproof and water control project in open-pit mines.At the same time,it also provides a reference for the survey of hidden disaster-causing factors of open-pit mines in grassland areas with fragile ecological environment.