Euphrates Poplar (Populus euphratica Oliv.) is a construction deciduous tree species in desert riparian forest and plays a vital role in ecological protection and sustainable floodplain management in arid regions. During a long period of time, the population growth structure has changed under the extreme drought environment under the water resources stress in the lower reaches of the Tarim River, and the forest stands spatial structure change is one of the obvious manifestations. Under the background of ecological water conveyance projects in this region over the past 20 years, it is necessary to find out the forest structure changes at present stage. Therefore, systematic study of the adaptability of P. euphratica population spatial distribution pattern and intraspecific competition under different water gradient conditions need to perform, which can deepen the understanding of the riparian forest adaptation mechanism to arid environment. In the present study, to investigate the intraspecies competition dynamics and spatial distribution patterns of P. euphratica under different water gradient conditions, three transects were selected at the Arghan area in the lower reaches of the Tarim River, NW China. Each transect was divided three research sites according to the water gradient. The results showed that: 1) the optimum competition range of P. euphratica in the lower Tarim River was 10 m; 2) The competition index and diameter at breast height (DBH) obtained the power function model (P<0.001). The competition index of P. euphratica decreased with the increase of the DBH, the competition index of the target tree gradually stabilized and remained at a low level, when the diameter at breast height of the target tree reached 20 cm or more; 3) The competition index of P. euphratica stands decreased with the decrease of the water gradient; 4) In the lower reaches of the Tarim River, the spatial distribution pattern of P. euphratica was mainly aggregated pattern, and with the increase of spatial scale, the distribution pattern gradually tended to random pattern; 5) With the decrease of water gradient, the spatial pattern of P. euphratica gradually changed from the aggregated to random distribution pattern. Water was the main factor determining the spatial distribution and structure of desert vegetation in extreme arid zones; In P. euphratica stand management, the relationship between interspecific competition, the spatial pattern and water gradient should be fully considered to provide an important scientific basis for the conservation and regeneration of the riparian forests in the lower reaches of the Tarim River.