Abstract: The Hulunbuir grassland area in Eastern China is an important coal and power base mainly with open-pit mining. In view of the insufficient research on the influence of open-pit coal mining on groundwater resources in Hu- lunbuir grassland area,the authors toke Baorixile open-pit mining area for this study,and divided the history of open-pit mining into three stages:initial stage,rapid increase stage and stable stage according to the characteristics of coal resources development and drainage intensity. By means of numerical simulation technology,the influence of drainage on the groundwater system in open-pit mining area was analyzed systematically. The simulation results show that in the first stage (initial period),due to the influence of drainage in the first mining area of Baori Sheller open-pit coal mine ( drainage intensity was 2. 3×104 m3 / d),the average water level drop in the mining area was less than 5 m. In the sec- ond stage (rapid increase period),Dongming open-pit mine on the west side of Baori Schiller open-pit mine was ex- ploited successively. As the loose aquifer near the surface of Dongming open-pit mine received sufficient recharge from surface water of Morigler river,the drainage intensity of the mining area increased to 19. 47×104 m3 / d,and the average water level in the mining area fallen more than 10 m. In the third stage ( stable period),after the closure of the first mining area in Baori Shiller open-pit mine,the No. 2 mining area had been exploited successively. However,the drain- age intensity of the whole mining area tended to be stable (14. 93×104 m3 / d),and the average water level drop in the mining area was more than 15 m. The loose medium aquifer groundwater recharged by river seepage was about 11． 02× 104 m3 / d,accounts for 80% of the drainage volume in Dongming open pit mine. Finally,according to the hydrogeolog- ical conditions of the study area,the characteristics of groundwater flow field under the curtain wall conditions,and the water inflow from aquifer under open pit mining conditions,the simulation model of groundwater system under the con- dition of curtain wall was constructed. The influence degree of curtain wall on drainage intensity was calculated and e- valuated which indicates that the drainage volume decreases to 6. 65×104 m3 / d and decrease range is about 51. 81%under the condition of 4 km long curtain wall. It can be seen that the curtain wall water-resisting and seepage-reducing technology is an effective mean of groundwater protection for the strong water-rich and strong recharge aquifers in the open-pit mining areas.