Taking Populus euphratica forests in extremely arid area as the research object, we studied the soil water movement and the ecological water consumption characteristics under different water conditions. The results showed that the HYDRUS-1D model had a good simulation effect on soil water movement and evapotranspiration in forestland in extremely arid regions. The soil water movement and ecological water consumption of Populus euphratica forests under different water conditions were significantly different. As the moisture condition of the underlying surface tended to be wet, the soil moisture content and the wetting front infiltration depth increased, and the infiltration depth reached 100 cm, 120 cm and 150 cm, respectively. The changes in moisture conditions on the underlying surface resulted in the changes in soil moisture storages. When the water supply of the underlying surface increased, the evapotranspiration of Populus euphratica forest increased significantly, and the transpiration increased significantly. The percentage of transpiration in the total evapotranspiration gradually increased from 55% to 65% as the moisture conditions became wet. Studies showed that with the gradual wetting of the underlying surface moisture conditions, the ecological water consumption of Populus euphratica forests in the extremely arid regions is gradually increasing, and transpiration is the main reason for the increase of water dissipation.