Understanding the effects of understory shrubs on dominant trees in plant communities and the water use strategies and interspecific relationships of communities is crucial for vegetation construction in arid areas. However, water niche derived from plant water use sources were not extensively explored. In this study, three typical native communities of Quercus liaotungensis (QL), Platycladus orientalis (PO) and Pinus tabulaeformis (PT) on the Loess Plateau were studied. Through continuous sampling of multiple soil depths and plant xylem water, combined with stable isotope technology, delta 2H and delta 18O values were analyzed. The MixSIAR model results showed that all species absorbed more shallow soil water (0-100 cm) in wet year (2021). The water use strategies of the three trees are different, i.e., PT absorbs more shallow soil water (0-100 cm, 54.73 % in study period) and PO absorbs more deep soil water (300-500 cm, 26.38 % in study period), while QL is in between (300-500 cm, 22.87 % in study period). The companion shrubs mainly use shallow soil water (67.39 %) and gradually transfer to the deep layer as the growing season progresses. Additionally, the niche breadth of each sampled plant in 2020 is higher than that in 2021, and the water niche overlap between species showed dynamic changes with the change of soil water on the annual scale. The water absorption ratio of all species was positively correlated with root length density, root surface area, root biomass, SWC (soil water content, 0-300 cm), while deep SWC showed different responses due to species differences. The results implied that PO showed stability in water use and was more adaptable to long-term water stress while PT was the most sensitive to water. The water absorption characteristics of QL were between the two. Our study provides new insights into species water use strategies and niche relationships in plant communities in arid and semi-arid regions.