Abstract: Numerical simulation of groundwater flow in the semiarid and semi humid climate of the Nebraska Sand Hills was made using the MODFLOW and the water balance model in the unsaturated zone.Analysis of groundwater recharge and dis charge and water balance in the aquifer reveal influences of unique topography of the sand dunes and soil property on ground water recharge and discharge.The simulation results demonstrate that the large infiltration rate of the sand soil results in much precipitation recharging into the aquifer,and thick unsaturated zone reduces groundwater evaporation losses.Therefore,sufficient groundwater could be stored in the thick aquifer,which maintains a steady streamflow and supplies numerous lakes and wet lands.This study is beneficial for groundwater resources evaluation and water resources protection in the environmentally vulnerable area of our country.