Water is the principal limited factor for plant growth in arid area. In this paper, Haloxylon ammodendron grows at inter-dune lowland and Haloxylon persicum grows at the sand dune were chosen, and stable oxygen isotopes technology was used to study the water sources of the two species of different diameter classes in the eastern Junggar Basin. The oxygen isotope ratios(δ¹⁸O) of xylem water of H.ammodendron and H.persicum of different diameter classes, soil water in different soil layers, and groundwater were measured. The MixSIAR model was used to calculate the possible ranges of potential water sources used by H.ammodendron and H.persicum, while graphical inference method and mean depth of water uptake model were used to determine the main soil layer absorbed by the two species. The results showed that soil water was the main water source for H.ammodendron of four different diameter classes. The Ⅰ(d ≤ 1 cm) diameter class of H.ammodendron mainly used shallow soil water(0-60 cm), with the possible contribution proportion of (45.4±10.9)%, and its water uptake soil depth was at 40-60 cm. The Ⅱ (1 cm < d ≤ 5 cm) and Ⅲ (5 cm < d ≤ 10 cm) diameter classes of H.ammodendron mainly used deep soil water(140-200 cm), with the possible contribution proportion of (40.7±11.5)% and (41.7±11.8)%, respectively, and their water uptake soil depth were all at 140-160 cm. The Ⅳ (10 cm < d) diameter class of H.ammodendron mainly used middle soil water (60-140 cm), with the possible contribution proportion of (42.0±9.2)%, and its water uptake depth was at 100-120 cm. With the increase of diameter, water use strategy of H.ammodendron was more flexible and tended to use shallow soil water. Soil water was the main water source for H.persicum of four different diameter classes. The Ⅰ(d ≤ 1 cm) diameter class of H.persicum mainly used shallow soil water(0-60 cm), with the possible contribution proportion of (40.5±10)%, and its water uptake soil depth was at 40-60 cm. The Ⅱ(1 cm < d ≤ 5 cm) diameter class of H.persicum mainly used middle soil water(60-140 cm), with the possible contribution proportion of (40.2±9.08)%, and its water uptake soil depth was at 100-120 cm. The Ⅲ(5 cm < d ≤ 10 cm) and Ⅳ(10 cm < d) diameter classes of H.persicum mainly used deep soil water(140-200 cm), with the possible contribution proportion of (40.0±12.2)% and (52.4±15.0)%, respectively, and their water uptake soil depth were at 160-180 cm and 180-200 cm, respectively. With the increase of diameter, H.persicum tended to use deep soil water. The two Haloxylon species had different water use strategies to adapt the arid environment.